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The principle of homeostasis in biology says that living organisms try to maintain some sort of equilibrium. Doing that requires the use of feedback mechanisms to regulate things like temperature, salinity, etc. Are there any feedback mechanisms the body uses to regulate the output of the skin's sebaceous glands? If so, what are they, and on what timescale do they operate?
Nice question! Unfortunately, the complete list of pathways involved in regulation of sebum production and secretion rate by sebaceous glands are not understood yet (Picardo et al, 2009). However, we know that sebum production is continuous and is not regulated by neural mechanisms (Thiboutot et al, 2004). Retinoids, hormones, and growth factors are known to influence sebaceous gland growth and differentiation (Zouboulis et al, 1998). Also, androgens and growth hormones are known to promote sebaceous gland differentiation (Deplewski et al, 1999, Rosenfield et al, 1998) whereas estrogens and retinoids, like 13-cis retinoic acid, inhibit their differentiation (Strauss et al, 1962).
In retinoids, isoretinoin is shown to have greater sebosuppressive action as compared to all-trans or 9-cis retinoic acid (Hommel et al, 1996). In androgens, androgen receptors have been localized to the basal layer of the sebaceous gland and the outer root sheath keratinocytes of the hair follicle, and testosterone and dihydrotestosterone are the major androgens that interact with these receptors (Liang et al, 1993). However, the molecular mechanisms through which androgens interact with these receptors and sebaceous glands are not understood yet (Thiboutot et al, 2004). Apart from this, insulin and Insulin-like Growth Factor 1 (IGF-1) also play a critical role here. Acne is considered as IGF-1 mediated disease, and high levels of sugar (caused due to diet) induce high levels of insulin and IGF-1. Both these hormones amplify the stimulatory effect of GH on sebocytes and augment mitogenic downstream signalling pathways of insulin receptors, IGF-1 receptor and fibroblast growth factor receptor-2b (Melnik et al, 2009).
Other (known) substances which are found to regulate sebum secretion include histamine (due to presence of H-1 receptor on sebocytes, Pelle et al, 2008), LXR ligands (due to presence of Liver X Receptor, Zouboulis et al, 2009), PPAR ligands (due to presence of Peroxisome Proliferator-Activated Receptor, Trivedi et al, 2006), vitamin D deficiency (Yildizgören et al, 2014), neuropeptides (Ganceviciene et al, 2009), etc. See the image below (from Makrantonaki et al, 2011) for visual representation:
In spite of this, elucidating the mechanism of regulation of sebum secretion by sebaceous glands is a difficult task since, although evidence suggests that nonendocrine factors may also be an important part for regulation along with endocrine factors, the nature of this secretion and the regulation of the secretory process seem to differ among the various types of glands which, in spite of being similar in structure, might be different in function and regulation (Thody et al, 1989).
1. Picardo, Mauro et al. “Sebaceous Gland Lipids.” Dermato-endocrinology 1.2 (2009): 68-71. Print.
2. Diane Thiboutot, Regulation of Human Sebaceous Glands, Journal of Investigative Dermatology, Volume 123, Issue 1, July 2004, Pages 1-12, ISSN 0022-202X, http://doi.org/10.1111/j.1523-1747.2004.t01-2-.x.
3. C.C. Zouboulis, L. Xia, H. Akamatsu, H. Seltmann, M. Fritsch, S. Hornemann, R. Ruhl, W. Chen, H. Nau, C.E. Orfanos The human sebocyte culture model provides new insights into development and management of seborrhoea and acne Dermatology., Volume 196, Issue 1, 1998, pp. 21-31
4. D. Deplewski, R.L. Rosenfield Growth hormone and insulin-like growth factors have different effects on sebaceous cell growth and differentiation Endocrinology., Volume 140, Issue 9, 1999, pp. 4089-4094
5. R.L. Rosenfield, D. Deplewski, A. Kentsis, N. Ciletti Mechanisms of androgen induction of sebocyte differentiation Dermatology., Volume 196, Issue 1, 1998, pp. 43-46
6. J.S. Strauss, A.M. Kligman, P.E. Pochi The Effect of Androgens and Estrogens on Human Sebaceous Glands J Invest Dermatol., Volume 39, 1962, pp. 139-155
7. L. Hommel, J.M. Geiger, M. Harms, J.H. Saurat Sebum excretion rate in subjects treated with oral all-trans-retinoic acid Dermatology., Volume 193, Issue 2, 1996, pp. 127-130
8. T. Liang, S. Hoyer, R. Yu Immunocytochemical localization of androgen receptors in human skin using monoclonal antibodies against the androgen receptor J Invest Dermatol., Volume 100, 1993, pp. 663-666
9. Melnik BC, Schmitz G. Role of insulin, insulin-like growth factor-1, hyperglycaemic food and milk consumption in the pathogenesis of acne vulgaris. Exp Dermatol. 2009;18:833-841
10. Edward Pelle, James McCarthy, Holger Seltmann, Xi Huang, Thomas Mammone, Christos C. Zouboulis, Daniel Maes, Identification of Histamine Receptors and Reduction of Squalene Levels by an Antihistamine in Sebocytes, Journal of Investigative Dermatology, Volume 128, Issue 5, May 2008, Pages 1280-1285, ISSN 0022-202X, http://doi.org/10.1038/sj.jid.5701160
11. Zouboulis, Christos C. “Sebaceous Gland Receptors.” Dermato-endocrinology 1.2 (2009): 77-80. Print.
12. Nishit R. Trivedi, Zhaoyuan Cong, Amanda M. Nelson, Adam J. Albert, Lorraine L. Rosamilia, Surendra Sivarajah, Kathryn L. Gilliland, Wenlei Liu, David T. Mauger, Robert A. Gabbay, Diane M. Thiboutot, Peroxisome Proliferator-Activated Receptors Increase Human Sebum Production, Journal of Investigative Dermatology, Volume 126, Issue 9, September 2006, Pages 2002-2009, ISSN 0022-202X, http://doi.org/10.1038/sj.jid.5700336
13. Yildizgören, Mustafa Turgut, and Arzu Karatas Togral. “Preliminary Evidence for Vitamin D Deficiency in Nodulocystic Acne.” Dermato-endocrinology 6.1 (2014): e983687. PMC. Web. 23 Apr. 2017.
14. Ganceviciene, Ruta et al. “The Role of Neuropeptides in the Multifactorial Pathogenesis of Acne Vulgaris.” Dermato-endocrinology 1.3 (2009): 170-176. Print.
15. Makrantonaki, Evgenia, Ruta Ganceviciene, and Christos Zouboulis. “An Update on the Role of the Sebaceous Gland in the Pathogenesis of Acne.” Dermato-endocrinology 3.1 (2011): 41-49. PMC. Web. 23 Apr. 2017.
16. Thody, A. J. & Shuster, S. Control and function of sebaceous glands. Physiol Rev 69, 383-416 (1989)
Identification and characterization of ABCB1-mediated and non-apoptotic sebum secretion in differentiated hamster sebocytes
Sebaceous glands secrete sebum onto the skin surface in a holocrine manner and as such a thin lipid layer is formed as a physiological barrier. In the present study, extracellular level of triacylglycerols (TG), a major sebum component, as well as intracellular TG accumulation was augmented in insulin-differentiated hamster sebocytes (DHS). The DHS exhibited phosphatidylserine exposure in an apoptosis-independent manner. In addition, intracellular ATP level and membrane-transporter activity using a substrate, Rhodamine 123, were highly detectable in the DHS rather than in the undifferentiated hamster sebocytes. A membrane-transporter activating reagent, 2′(3′)-O-(4-benzoylbenzoyl) adenosine 5′-triphosphate (BzATP), enhanced transporter activity, extracellular TG level, and phosphatidylserine exposure in the DHS. Both transporter activity and TG secretion were suppressed by R-verapamil, a potent membrane-transporter inhibitor, in the BzATP-treated and untreated DHS. Furthermore, the gene expression and production of ATP-binding cassette subfamily B member 1 (ABCB1) were augmented in the DHS. ABCB1 was also detectable in sebaceous glands in the skin of hamsters. Moreover, the cell-differentiation- and BzATP-augmented transporter activity and TG secretion were dose-dependently inhibited by adding not only an ABCB1 antibody but also a selective inhibitor of ABCB1, PSC833. Thus, these results provide novel evidence that ABCB1 is involved in sebum secretion in the DHS, which is associated with non-apoptotic phosphatidylserine exposure and the increased level of intracellular ATP. These findings should accelerate the understanding of sebum secretion occurring in a holocrine-independent manner in sebaceous glands, and may contribute to the development of therapies for sebaceous gland disorders such as acne, seborrhea, and xerosis.
►Sebocyte differentiation results in the augmentation of sebum secretion. ►Differentiated sebocytes exhibit apoptosis-independent PS exposure. ►Increase in ATP level and transporter activity in differentiated sebocytes. ►ABCB1 expression is augmented in differentiated sebocytes. ►Involvement of ABCB1 in sebum secretion in differentiated sebocytes.
The sebaceous glands, each attached to a hair follicle, produce sebum through a process called holocrine secretion. The glands produce lipids, which remain inside the sac-like glands for about a week until the sac erupts, allowing the sebum to flow freely into the hair follicle. The hair then wicks the oil onto the skin to lubricate and protect it.
All babies are born with sebaceous glands over most of their bodies, with the exception of the palms of the hands, tops and soles of the feet, and lower lips.
These glands produce significant amounts of sebum right after birth. This is because the glands are regulated by hormones, particularly androgens (male sex hormones such as testosterone), which newborns have in abundance.
As a baby reaches toddlerhood, their hormone levels even out and the sebaceous glands become less active: Children produce very little sebum between ages 2 to 6. With the approach of puberty, androgens again flood the body and the glands pump out steady amounts of sebum.
Sebum production starts to decrease by age 20 and continues to slow with age.
The face, scalp, upper neck, and chest host the most sebaceous glands, so when there's a surge in sebum production, these areas are prone to acne breakouts or oily skin.
The size of these glands and the way hormones influence them are determined by genetics, so if you have close relatives with acne, dry skin, or other sebum-related conditions, you're more likely to suffer from the same problem.
Neuroendocrinology and neurobiology of sebaceous glands
The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro-regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α-melanocyte-stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro-autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin-mediated or facial paresis-associated reduction of human sebum secretion suggests that cutaneous nerve-derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin.
Keywords: acne vulgaris androgens hormones nervous system neuroendocrinology neurons neuropeptides sebaceous gland sebum skin.
the elaboration and release of secretions by glandular cells. While performing its vital activities, every cell of an organism forms several metabolic products, releasing them either into the external or internal environment. When the secretory function is the basic function of a group of specialized glandular cells it is called secretion. External, or exocrine, secretion is distinguished from internal, or endocrine, secretion. In external secretion the products elaborated by a gland are released into the external environment the secretion first enters the glandular duct, from which it is discharged onto the surface of the body or into hollow organs. In internal secretion (incretion) synthesized substances are released into the blood or lymph.
The secretory cycle of any gland has both a production (biosynthesis) phase and a release phase. The term &ldquosecretion&rdquo is sometimes applied only to the latter phase. In some glands the phases occur simultaneously the phases occur at different times in glands whose phases are regulated by different specific mechanisms. The secretion process resembles an intracellular conveyor system, in which the synthesized product gradually matures and steadily moves with the cell from one organoid to another. The initial products, including amino acids, monosaccharides, fatty acids, and salts, are absorbed from the blood and tissue fluid by a glandular cell.
The biosynthesis of the secretion (especially of protein products) starts in the endoplasmic reticulum, where the amino acids, which have been adsorbed on the cellular membranes, are joined together in a sequence determined by the messenger RNA of ribosomes. The synthesized initial product accumulates in the fissures and lacunae of the endoplasmic reticulum, from which it shifts to the area of the laminar Golgi complex, where the maturation of a secretion is completed. In the area of the Golgi complex in some glandular cells the synthesized protein combines with carbohydrates and the secretion is converted into a glycoprotein. Mitochondria, which are numerous in glandular cells, produce the energy needed to synthesize and release a secretion. The synthesis of secretions of a lipidic (steroid) nature is completed on the mitochondria.
In the phase of secretion release increases are observed in oxygen consumption by the glandular cells, intracellular osmotic pressure, and the amount of water entering the cells. The result is the establishment in a glandular cell of a stream of water, which enters through the base of the cell and emerges through the apical membrane. Flowing through the cytoplasm, the water picks up the accumulated secretion and releases it from the cell, either in the form of a solution that is diffused through the apical membrane or in the form of drops that are passed through membrane pores. During this type of secretion, which is called merocrine secretion, glandular cells do not suffer any damage. If, however, the secretion is insoluble in water or for some other reason is incapable of passing through the apical membrane, the intensified passing of water into a swelling glandular cell causes the apex of the cell with its accumulated granules or drops of secretion to swell clavately and then rupture or be detached.
The liberation of secretion by the detachment of the apex of a glandular cell without the cell&rsquos destruction is called apocrine secretion. Sometimes this type of secretion is limited to the swelling and detachment of microvilli from a glandular cell (microapocrine secretion). Occasionally, while a glandular cell is degenerating, it is completely transformed into a drop of secretion and is ejected from the epithelial layer into the lumen of the gland this type of secretion is called holocrine secretion. In the course of evolution, holocrine secretion, which is a primitive type of secretion, has been replaced by merocrine secretion, which is more effective.
Both phases of the secretory cycle are regulated by the combined or successive influences of several neural and humoral factors. The nerve fibers that carry impulses stimulating secretion to the glands are called secretory fibers. The neural effects that are manifested by the intensified elaboration of secretion during the production phase are called trophic effects. There is no clear distinction between secretory and trophic nerves because the stimulation of a fiber that innervates a gland causes both secretory and trophic effects. Glandular activity is also influenced by humoral agents, including some hormones (especially those involved in regulating the functions of the endocrine glands). For example, the thyrotropic, gonadotropic, and adrenocorticotropic hormones of the anterior pituitary excite, respectively, the thyroid gland, the ovaries and testes, and the adrenal cortex (the glucocorticoid function). Secretin, which is produced in the duodenal mucosa, stimulates the release of pancreatic juice by the acinar cells of the pancreas.
Besides hormones, other substances formed in the body may also affect glandular function. Histamine, for example, sharply intensifies the secretion of the fundic glands of the stomach. The effect of humoral stimulants is manifested in both phases of the secretory cycle. Certain ions directly affect the secretion of many glands an excess of monovalent cations (K + or Na + ) usually intensifies secretion, whereas bivalent ions (Ca 2+ and Mg 2+ ) weaken secretion. The stimulation of a glandular cell is based on the activation of adenyl cyclase, an enzyme localized in the cell&rsquos surface membrane. Adenyl cyclase acts as a stimulus in the formation of cyclic adenosine monophosphate, which regulates the chain of intracellular reactions resulting in the increased activity of the specific enzyme systems causing secretion. The large number of factors influencing secretion is explained by the fact that they are all equally capable of activating the adenyl-cyclase mechanism of the glandular cell. Nerve cells are also characterized by secretory activity they all elaborate and release mediators, and in neurosecretory cells the production of physiologically active substances called neurohormones reaches a high level of intensity.
Hormonal Responses to Food
The endocrine system controls the release of hormones responsible for starting, stopping, slowing, and quickening digestive processes.
Describe hormonal responses to food
- The presence and absence of hormones that are released into the bloodstream generate specific digestive responses they either stimulate or discontinue digestive processes.
- In hormone control, a negative feedback mechanism takes place when the stomach is empty and its acidic environment does not need to be maintained as a result, a hormone is released to stop the release of hydrochloric acid, which was previously activated to aid digestion.
- In some cases, hormones work in tandem and sequentially to achieve important digestive functions, such as in the breakdown of acidic chyme, where hormones act in releasing the appropriate secretions in the appropriate stages of digestion.
- When digesting certain types of foods, such as ones high in fat, hormones can control the speed of food digestion and, therefore, absorption.
- endocrine system: a control system of ductless glands that secrete hormones which circulate via the bloodstream to affect cells within specific organs
- chyme: the thick semifluid mass of partly digested food that is passed from the stomach to the duodenum
- secretin: a peptide hormone, secreted by the duodenum, that serves to regulate its acidity
- cholecystokinin: any of several peptide hormones that stimulate the digestion of fat and protein
- somatostatin: a polypeptide hormone, secreted by the pancreas, that inhibits the production of certain other hormones
- gastrin: a hormone that stimulates the production of gastric acid in the stomach
Hormonal Responses to Food
The endocrine system controls the response of the various glands in the body and the release of hormones at the appropriate times. The endocrine system’s effects are slow to initiate, but prolonged in their response, lasting from a few hours up to weeks. The system is made of a series of glands that produce chemicals called hormones. These hormones are chemical mediators released from endocrine tissue into the bloodstream where they travel to target tissue and generate a response.
One of the important factors under hormonal control is the stomach acid environment. During the gastric phase, the hormone gastrin is secreted by G cells in the stomach in response to the presence of proteins. Gastrin stimulates the release of stomach acid, or hydrochloric acid (HCl), which aids in the digestion of the majority of proteins. However, when the stomach is emptied, the acidic environment need not be maintained and a hormone called somatostatin stops the release of hydrochloric acid. This is controlled by a negative feedback mechanism.
In the duodenum, digestive secretions from the liver, pancreas, and gallbladder play an important role in digesting chyme during the intestinal phase. In order to neutralize the acidic chyme, a hormone called secretin stimulates the pancreas to produce alkaline bicarbonate solution and deliver it to the duodenum. Secretin acts in tandem with another hormone called cholecystokinin (CCK). Not only does CCK stimulate the pancreas to produce the requisite pancreatic juices, it also stimulates the gallbladder to release bile into the duodenum.
Digestive endocrine system: Hormones, such as secretin and cholecystokinin, play important roles in digestive processes. These hormones are released from endocrine tissue to generate specific controls in the digestion of chyme. As seen in the image, hormones are vital players in several bodily functions and processes.
Another level of hormonal control occurs in response to the composition of food. Foods high in lipids (fatty foods) take a long time to digest. A hormone called gastric inhibitory peptide is secreted by the small intestine to slow down the peristaltic movements of the intestine to allow fatty foods more time to be digested and absorbed.
Understanding the hormonal control of the digestive system is an important area of ongoing research. Scientists are exploring the role of each hormone in the digestive process and developing ways to target these hormones. Advances could lead to knowledge that may help to battle the obesity epidemic.
Other files and links
In: Thrombosis and Haemostasis , Vol. 86, No. 5, 2001, p. 1148-1155.
Research output : Contribution to journal › Review article › peer-review
T1 - Regulated secretion in endothelial cells
T2 - Biology and clinical implications
N2 - Vascular endothelial cells are critical participants in maintaining blood flow, with the ability to respond rapidly to injury. We have outlined above how the regulated secretion of a variety of hemostatic and inflammatory mediators contributes to these nearly instantaneous responses. The WPB are the most prominent of these regulated secretory granules, and there is growing evidence of additional granules that release their contents under a variety of conditions. The mechanisms responsible for the targeting of proteins to regulated secretory granules, and of exocytosis of these granules are being elucidated. EC appear to share some characteristics with other secretory cell types, but also are likely to have unique properties related to the storage and secretion of large multimeric proteins such as VWF and multimerin. Understanding these mechanisms may lead to new strategies for treating coronary artery disease, stroke, sickle cell disease, and hemophilia through drugs that modulate sorting and secretion, or by gene transfer approaches that introduce therapeutic molecules into the WPB for regulated release.
AB - Vascular endothelial cells are critical participants in maintaining blood flow, with the ability to respond rapidly to injury. We have outlined above how the regulated secretion of a variety of hemostatic and inflammatory mediators contributes to these nearly instantaneous responses. The WPB are the most prominent of these regulated secretory granules, and there is growing evidence of additional granules that release their contents under a variety of conditions. The mechanisms responsible for the targeting of proteins to regulated secretory granules, and of exocytosis of these granules are being elucidated. EC appear to share some characteristics with other secretory cell types, but also are likely to have unique properties related to the storage and secretion of large multimeric proteins such as VWF and multimerin. Understanding these mechanisms may lead to new strategies for treating coronary artery disease, stroke, sickle cell disease, and hemophilia through drugs that modulate sorting and secretion, or by gene transfer approaches that introduce therapeutic molecules into the WPB for regulated release.
Anatomy diagram source
They are holocrine glands ie the sebum consists of the entire secreting cells. Sebum the oily secretion of the sebaceous glands whose ducts open into the hair follicles.
Human Skin Sebaceous Gland Human Body Png Clipart Adipose
Since sebaceous glands secrete their oil into ducts before reaching the surface of the skin they are considered exocrine glands.
Sebum definition anatomy. In humans they occur in the greatest number on the face and scalp but also on all parts of the skin except the palms of the hands and soles of the feet. Sebaceous gland small oil producing gland present in the skin of mammals. Sebum is made up of triglycerides free fatty acids wax esters squalene cholesterol esters and cholesterol.
Sebum is a light yellow oily substance that is secreted by the sebaceous glands that help keep the skin and hair moisturized. Sebaceous glands are numerous microscopic glands in the dermis that usually open into the hair follicles and secrete sebum. Sebum synonyms sebum pronunciation sebum translation english dictionary definition of sebum.
This oil lubricates the skin and scalp of mammals. Sebaceous glands are usually attached to hair follicles and release a fatty substance sebum into the follicular duct and thence to the surface of the skin. Any of the small sacculated glands lodged in the substance of the derma usually opening into the hair follicles and secreting an oily or greasy material composed in great part of fat which softens and lubricates the hair and skin.
N the oily secretion of the sebaceous glands. In the eyelids meibomian glands also called tarsal glands are a type of sebaceous gland that secr. It is composed of fat and epithelial debris from the cells of the malpighian layer and it lubricates the skin.
The type of secretion of the sebaceous glands is referred to as holocrine. An oily secretion of the sebaceous gland which helps to preserve the flexibility of the hair. Medical definition of sebaceous gland.
Sebaceous gland plural sebaceous glands anatomy a gland of the skin which secretes an oily substance sebum usually into a hair follicle near the surface of the skin. The semifluid secretion of the sebaceous glands consisting chiefly of fat keratin and cellular material. Sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter called sebum to lubricate and waterproof the skin and hair of mammals.
The waxy oil that is secreted into the hair follicles is called the sebum.
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Sebum, Sweat, Skin pH and Acid Mantle
Sebum is an oily secretion produced by sebacious glands, tiny ducts adjacent to hair follicles. Sebum is secreted into the follicle, from which it spreads over the hair and skin. The main role of sebum is to waterproof the skin and hair. Both excess and lack of sebum are undesirable. Excess sebum is associated with oily skin and acne. It is particularly common in adolescents as the increased levels of sex hormones stimulate sebum production. Lack of sebum, which is common in middle and older age, leads to skin dryness and accelerates wrinkle formation.
Sweat is a salty, watery solution produced by sweat glands, numerous microscopic channels opening onto the skin surface. As sebum and sweat mix up on the skin surface, they form a protective layer often referred to as the acid mantle . Acid mantle has a particular level of acidity characterized by pH from about 4 to 5.5. A pH of 7 is considered neutral, above 7 is alkaline, and below is acidic. The pH of acid in the human stomach, for example, is usually from 1 to 2, which is highly acidic. The skin, on the other hand, is mildly acidic. In addition to helping protect skin from "the elements" (such as wind or pollutants), acid mantle also inhibits the growth of harmful bacteria and fungi. If acid mantle is disrupted or loses its acidity, the skin becomes more prone to damage and infection. The loss of acid mantle is one of the side-effects of washing the skin with soaps or detergents of moderate or high strength.