198 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Very low numbers of organisms can be recovered from the shafts of axillary hairs. These are probably displaced from the surface. Although odor is more intense in an unshaved axilla, the hairs serve mainly to disperse the preformed odor (9). When individuals were classified as to whether they had intense, typical apocrine (acrid) odor or the distinctively different "acid" odor, interesting differences were found with respect to the composition of the microflora. First of all those individuals with strong odor had 2 to 3 times as many organisms. There were differences in the representation of diphtheroids between these two odor groups. Every subject with an acrid odor had lipophilic diphtheroids compared to about a 50% prevalence in the acid group. Moreover, the mean density in the latter group was only 50,000/cm 2 in contrast to an average of 800,000/cm 2 in the group with acrid odor. In regard to large colony diphtheroids, the difference between the two groups was also striking but numerically of lesser magnitude. About 50% of acrid odor producers were colonized by these particular diphtheroids (mean--250,000/cm 2) compared to 9% of the acid group (mean--1500/cm•). These findings point unmistakeably to diphtheroids as the source of the acrid apocrine odor, especially the lipophilic ones, invariably present in high numbers in these subjects. These relationships are summarised in Fig. 1. The controlling role of diphtheroids in producing this odor was confirmed in an in vivo experiment (22a). Droplets of apocrine sweat were placed on forearms after deferming with 70% ethanol. To this was added 0.1 ml of suspensions containing 2 x 10 • cells of 7.0 6.0 I APOCRINE ODOR NON APOCRINE ODOR 5.0 4.0 o 5.0 2.0 1.0 m MICROCOCCI [•m LIPOPHILIC DIPTHEROIDS i•:[] LARGE COLONY DIPTHEROIDS [] GRAM NEGATIVE RODS [] PROPIONIBACTERIA o Figure 1. Diphtheroids as the source of the acrid apocrine odor.

PERSPECTIVES ON AXILLARY ODOR 199 various organisms found in the axilla. The sites were then occlusively covered for 24 hours to ensure multiplication of the organisms. The odor was then assessed organoleptically by three blind observers. Both types of diphtheroids produced intense odor in every instance where their numbers reached 10,000/½m 2. When resident cocci (S. epidermidis and S. saprophyticus) were incubated with apocrine secretion, the acrid apocrine odor was not produced. Instead, a sweaty, acid odor was generated similar to that of isovaleric acid whose presence was demonstrated in a separate study. Gram negatives created odors quite distinctive from either of the above odors. Magnesium- omadine, an antibacterial, reduced bacterial growth and thus all bacterially derived odors. Additionally, some diphtheroids after repeated subcultivation failed to generate strong odors on incubation with apocrine secretion. This explains lack of odor in some cases with good bacterial growth. Jackman has also confirmed the presence of two distinct types of axillary flora with the coryneforms being higher in males and contributing the more pronounced body odor (22b). BIOCHEMICAL ASPECTS OF AXILLARY ODOR The axillary odor has been described in astonishingly different ways. The characteriza- tions include: goat-like, over-ripe peaches, chlorinared urine, burnt coffee-beans, ammoniared Valerian, etc. These quixotic designations reveal the inadequacy of subjective perceptions and the fact rhar at least two odor types are being described. With the advent of combined gas chromatography-mass specrromerry and radioimmu- noassay techniques ir becomes possible ro investigate the composition of apocrine secretion and ro identify the odor chemicals. Samples of the axillary surface lipids contain considerably more cholesterol and cholesterol esters than surface lipids from other sebum rich areas such as the face (Table V). This reflects the high concentration of free cholesterol in apocrine secretion itself. Various sreroidal substances have been identified in samples from the axilla, usually collected in pads held in the axillary vault (Table VI). The two A•6-androgen steroids, 5o•-androsr-16-en-3-one, a kerone, and 5o•-androsr-16-en-3o•-ol, an alcohol, together account for parr of the acrid axillary odor. The latter has a musky odor and is nor altogether unpleasant (Table III). The kerone confers the disagreeable and Table V Axillary and Apocrine Lipid Profiles Percent Composition Glandular Secretion Apocrine • Sebaceous 2 Extract Skin Surface Axillae Facial Cholesterol 76.2% 3.4% 8.9% 1.5% Cholesterol Esters 0.9%* 21.8% 8.8% 3.0% Wax Esters 3.6%* 21.2% 26.0% Squalene 0.2%* 19.0% 13.4% 12.0% Glycerides and Fatty Acids 19.2%* 55.9% 47.4% 57.5% Total Lipid 20 3tg/3tl -- 60 3tg/cm 2 100 3tg/cm 2 Protein 90 3tg/3tl -- -- -- •Stimulated and collected at skin surface •Collected from microdisection of gland (39) *Probably of sebaceous origin