Advances in Fingerprint Technology.pdf

Table 3.4 The Approximate Composition of Sebum
and Surface Epidermal Lipids
Constituent
Sebum
(wt%)
Surface epidermal lipid
(wt%)
Glyceride/free fatty acids 57.5 65
Wax esters 26.0 —
Squalene 12.0 —
Cholesterol esters 3.0 15
Cholesterol 1.5 20
Source: Downing, D. T. and Strauss, J. S., Synthesis and composition
of surface lipids of human skin, J. Invest. Dermatol., 62, 231,
1974. With permission.
that maximum stimulation of the sebaceous glands is accomplished by
endogenous testosterone. Other studies have found slight increases in skin surface
lipids after administering testosterone. 49 Testosterone given to children also
produced a significant increase in sebum production. 50 Metabolism and elimination
of these compounds in human skin samples has been reported. 51 It
appears that excretion of C 19- and C 18-steroids through the skin may exceed
their urinary elimination.
Lipid Origin and Breakdown
Radioactive labeling studies have illuminated the formation and origin of
lipids. 52 Autoradiograms from one study showed that radioactivity (from
incubating samples of subcutaneous fat from scalp biopsies with [ 14 C] acetate)
found in total lipid extracts was confined to squalene, wax esters, triglycerides,
and phospholipids. It is significant to note that cholesterol,
cholesterol esters, and free fatty acids did not contain any significant amount
of radioactivity. That would imply that these compounds are of epidermal
origin rather than being produced in the sebaceous gland. The differences
in lipid classes between lipids of sebaceous and epidermal origin are listed
in Table 3.4. Another study proposed that sebaceous lipids are derived from
two different sources, the body’s circulation (exogenous lipid) and from de
novo synthesis (endogenous lipids). 53 They assumed that the composition of
both of these sources remained constant, but that their relative contribution
to sebum was variable. Examples of possible exogenous lipids would include
linoleate (an essential fatty acid), cholesterol, cholesterol esters, and triglycerides.
However, the fact that circulating cholesterol esters and triglycerides
have different fatty acid compositions than their sebaceous counterparts
makes it unlikely that they are incorporated directly into sebum. Examples
of endogenous lipids that are not available from blood include ∆6 fatty acids,
squalene, and wax esters.