according under endocrine control and so the sebum

according to there location in the body,
as well as among individuals, ethnic groups and according to sex and age.33,39(Susan standring,
Harold Ellis, Jeremih C Healy, Debit Johnson Endrew Williams petricia Collins,
et al. gry`s Anatomy. 39th ed. Elsevier Churchill Livingstone: 2005:
Pp 15,7.)

Sebum

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Sebum is a lipid rich substances
secreted by the sebaceous gland.The sebaceous gland is holocrine in that it
forms its secretion by the complete disintegration of the glandular cells.The
normal function of sebum are the provision of a protective coating on hairs,
possibly helping to waterproof the epidermis,discouragement of ectoparasites
and contribution to a characteristic body odour.33(Susan standring,
Harold Ellis, Jeremih C Healy, Debit Johnson Endrew Williams petricia Collins,
et al. gry`s Anatomy. 39th ed. Elsevier Churchill Livingstone: 2005:
Pp 15,7.) When first formed, sebum is a complex mixture of over 50%
di and triglycerides with smaller proportion of wax esters. Squalene,
cholesterol esters, cholesterol and free fatty acids.Sebum is slightly
acidic(pH 4.2-5.6).39(Lawrence Charles Parish. Sarah Brenne, Maria Romos. Womens
Dermatology from infancy to maturity. The Parthenon publishing group (London):
Pp 109-10.)

NORMAL VARIATION IN SEBUM PRODUCTION AND
EXCRETION- AGE AND SEX

The sebaceous glands are under endocrine
control and so the sebum production 
varies with age and sex. The sebaceous glands are well developed at end
of fetal life, but after birth the size rapidly reduces.33,39(Susan standring,
Harold Ellis, Jeremih C Healy, Debit Johnson Endrew Williams petricia Collins,
et al. gry`s Anatomy. 39th ed. Elsevier Churchill Livingstone: 2005:
Pp 15,7.) They enlarge and 
become functional again after puberty.33(Susan standring, Harold Ellis, Jeremih C
Healy, Debit Johnson Endrew Williams petricia Collins, et al. gry`s Anatomy. 39th
ed. Elsevier Churchill Livingstone: 2005: Pp 15,7.) Males have a
significantly greater sebum excretion rate then females, excretion rate then
females expect in the age group 10-15 years. This is probably explained by the
earlier development of puberty in the female.Sebum excretion rate continues to
increase after puberty, reaching the peak in both sexes between 30-40
years.Thereafter there was a gradual decline at the menopause.33(Susan standring,
Harold Ellis, Jeremih C Healy, Debit Johnson Endrew Williams petricia Collins,
et al. gry`s Anatomy. 39th ed. Elsevier Churchill Livingstone: 2005:
Pp 15,7.)Beginning in young adulthood there is an age related
decline in wax ester secretions. Thus hormones also affect the composition of
sebum. The fatty acid composition of sebum is affected by androgens in both sexes.39(Lawrence Charles
Parish. Sarah Brenne, Maria Romos. Womens Dermatology from infancy to maturity.
The Parthenon publishing group (London): Pp 109-10.)

HORMONES INFLUENCING SEBUM PRODUCTION

1.Androgens

The skin is a major site of androgens
metabolism and primary target for the effects of androgens.Androgen steroids of
either gonadal or adrenal origin have a direct stimulatory effect on sebaceous
gland activity.Mitotic activity,intracellular lipid synthesis and the thickness
of the epidermis increases.40(Gred Plewig, Albert M
Klingman. Acne and Rosacea. 2nd ed. Springer-Verlag Heidel berg
(Germeny): 1993: Pp, 39-43.)Circulating androgen levels alone could
not account for the difference in the mean levels of excretion between the
sexes, as there is a wide degree of overlap between men and women in their
sebum excretion rate.39(Lawrence Charles Parish. Sarah Brenne, Maria Romos. Womens
Dermatology from infancy to maturity. The Parthenon publishing group (London):
Pp 109-10.)

 

Blood testosterone levels of women are
one tenth those of men, but in a third of women sebum excretion rates are as
high as the mean for men.Although androgens are essential for providing adult
levels of sebum, additional factors are operative.39(Lawrence Charles
Parish. Sarah Brenne, Maria Romos. Womens Dermatology from infancy to maturity.
The Parthenon publishing group (London): Pp 109-10.)Androgen
receptors have been identified in sebaceous glands, using mouse monoclonal
antibodies against the N-termi-terminal region of human androgen receptor.41(Choudhry R,
Hodgins MB, Van der Kwast TH, AO Brinkmann, WJ Boersma. Localization of
androgen receptor in human skin by immunohistochemistry: implications for the
hormonal regulation of hair growth, sebaceaous glands and sweat glands J
Endocrinol 1992: 133: 467-75.)Androgen receptors have also been
identified in basal and

Differentiating sebocytes, and their
concentration was found to be higher in males than in females. They have also
been found in pilosebaceous duct keratinocytes suggesting that androgen
influence pilosebaceous duct keratinisation.39(Lawrence Charles Parish. Sarah Brenne, Maria
Romos. Womens Dermatology from infancy to maturity. The Parthenon publishing
group (London): Pp 109-10.)

 

2. Estrogens

 

Decrease the sebum production they do
not significantly affect the proliferation of sebaceous gland. They may act
either by suppressing the secretion of pituitary gonadotrophins and hence the
production of androgen or by enhancing the binding of testosterone to
testosterone binding globulin40.(Gred Plewig, Albert M Klingman. Acne and Rosacea. 2nd
ed. Springer-Verlag Heidel berg (Germeny): 1993: Pp, 39-43.)

 

3. Pituitary hormones

 

The anterior pituitary gland plays an
important role in the control of sebaceous glands. They increase the sebum
production. Most of the hormones ( TSH, ACTH, FSH and LH ) act indirectly by
stimulating their respective endocrine 
tissues. In other cases the hormones ( for instance growth hormone ) act
synergistically with another hormone to which the sebaceous gland is sensitive.32(Robert Baran. Text
book of Cosmetic Dermatology. Taylur and Frances Publication; 1998: P 23.)

 

Other Factors influencing sebum
production

 

Genetic factor

Familial occurrence of acne vulgarise ,
seborrhoea parents normally generate seborrhoea children, similar sebum
excretion rates in identical twins indicate the genetic component involved in
control of sebum production40.(Gred Plewig, Albert M Klingman. Acne and Rosacea. 2nd
ed. Springer-Verlag Heidel berg (Germeny): 1993: Pp, 39-43.)

 

2 AGE

In newborns sebum production is high; it decreases
from the second month onwards to the end of the first year of life.Sebum
excreation markedly increase at puberty with its highest levels in acne
patients. In adulthood it gradually decreases.40(Gred Plewig, Albert M Klingman. Acne and
Rosacea. 2nd ed. Springer-Verlag Heidel berg (Germeny): 1993: Pp,
39-43.)

3 Temperature

Changes in skin temperature influence the sebum
excretion rate by about 10% per degree Celsius.Sebum secretion seems to follow
a circadian rhythm, being highest during the first hour of sleep and to
increase in the summer months.

4 DIET

Diet has no influence on sebaceous activity.

5 SWEATING

It is only the appearance of oiliness which is
increase by sweating.

6 INNERVATION

Sebaceous
secreation is not under neural control.Specialized sebaceous gland like
the  meibomian gland of the eyelid have
innervations.40(Gred Plewig, Albert M Klingman. Acne and Rosacea. 2nd
ed. Springer-Verlag Heidel berg (Germeny): 1993: Pp, 39-43