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The hypothesis that sebum permits the growth of Pityrosporum ovale, and hence the development of seborrhoeic dermatitis, was tested by observing whether a reduction of sebum production by isotretinoin would improve the disorder. In 10 male patients with seborrhoeic dermatitis, treatment with isotretinoin for 6 weeks reduced the mean sebum excretion rate by 70% and improved the severity of the rash, but with a site difference in magnitude of response. It is concluded that the residual pool of sebum is important for the growth of P. ovale and that, within the physiological range, sebum has a permissive effect on the growth of this yeast. Variation in the pools of residual sebum explains a number of features of the disease such as site of involvement and greater prevalence in males than females. The pathological increase in the residual pool of sebum due to immobility explains the frequent occurrence of seborrhoeic dermatitis in patients with a variety of neurological disorders.

Cyproterone acetate, applied as 1% solution in ethanol or isopropyl myristate, did not decrease the sebum excretion rate (SER) when applied to forehead skin of patients with acne, although SER is decreased when the drug is given systemically. The probable explanation is that cyproterone acetate owes its local action to a metabolite formed systemically. The present study shows this is unlikely to be the 17 beta-hydroxy cyproterone acetate.

The sebum excretion rate has been found to be increased in female patients with phenylketonuria. This may be related to a depletion of midbrain dopamine and release of the sebotrophic hormone.

The effect of progesterone on the rate of sebum secretion was examined in intact and gonadectomized rats. In intact, adult, male rats, progesterone administered for 3 weeks decreased sebum secretion; after castration of adult males, progesterone increased sebum secretion and an even greater response occurred in male castrated at 21 days of age. In intact, adult, female rats progesterone slightly increased sebum production. As in the male, the response was affected by the time of gonadectomy, a greater response occurring after spaying at 21 days compared with 10 weeks of age. Thus, the response to progesterone in the adult rat differs in intact males and females and is affected by changes in the endocrine environment induced by gonadectomy, especially near the time of puberty.

Sebum excretion rates (SER) were measured before and after treatment in patients with hypothyroidism and thyrotoxicosis. The mean SER in the former was significantly less than that in normal controls but there was no correlation between SER and the severity of the disease as indicated by serum thyroid-stimulating hormone levels. After treatment with L-thyroxine the SER increased but remained subnormal. By contrast the SER was not increased in patients with thyrotoxicosis and it was unaffected by treatment. The human sebaceous gland seems to respond to thyroid hormone mainly in the hypothyroid range.

17 alpha Propyltestosterone produced a mean inhibition of sebum excretion of 20% when it was applied topically for four weeks to the forehead skin of patients with acne.

The sebum-excretion rate (S.E.R.) has been found to be increased in patients with benign as well as malignant breast disease. The S.E.R. was not increased in patients undergoing surgery for other diseases. It is considered that the sebotrophic hormone may also be mammotrophic. Drugs such as reserpine and the phenothiazines which increase sebum production may perhaps provoke benign as well as malignant breast disease.

The effect of progesterone on the rate of sebum secretion was examined in intact and gonadectomized male and female rats. In intact adult male rats, progesterone administered for 3 weeks decreased sebum secretion, whereas in intact adult female rats, progesterone slightly increased sebum production. In castrated adults progesterone increased sebum secretion in both sexes, a greater response occurring after castration at 21 days of age than after castration at 10 weeks. Thus, the response to progesterone in the adult rat differs in intact males and females and is affected by changes in the endocrine environment induced by gonadectomy, especially near the time of puberty.

Sebum secretion was measured in adult female and male rats given alpha-melanocyte stimulating hormone (alpha-MSH) during early life. Daily treatment with 40 microgram alpha-MSH/100 gm body weight for the first 5 weeks of life increased sebum secretion in female and male rats at 8, 11, and 15 weeks of age. A lower dose of alpha-MSH (10 microgram/100 gm body weight) produced similar changes in male but not in female rats. No effect on sebum secretion was found in female and male rats aged between 8-28 weeks when alpha-MSH was given (1) from the day of birth to 3 weeks; (2) 3--5 weeks; (3) 1st and 5th weeks and (4) 7--12 weeks. Apparently alpha-MSH must be given throughout the first 5 weeks of life in order to produce a sustained effect on the sebaceous glands. The fact that males appear to be more sensitive than females, in that they responded to a lower dose of alpha-MSH, may indicate that MSH acts by enhancing the response to androgen. Early alpha-MSH treatment failed to alter the sebaceous gland response to testosterone in adult female and male rats but the possibility that alpha-MSH enhances the action of androgen in early life cannot be ruled out.

The sebum excretion rate (SER) in forehead skin was measured in late pregnancy and 8-20 weeks after delivery in 43 women. There was considerable individual variation but the mean SER during pregnancy was significantly higher than in a control group of non-pregnant women and it showed a large and significant decrease to the control level after delivery. This suggests that a powerful sebotrophic hormone is secreted during pregnancy. The mean SER during pregnancy in women with twins or triplets was no greater than the SER in women with a single foetus. This suggests that the sebotrophic factor of pregnancy is unlikely to be of placental origin, and is in keeping with the idea that the sebotrophic factor may come from the pituitary.

The effect of alpha-MSH on sebum secretion and preputial gland weight was examined in intact, castrated and hypophysectomized male rats and in hypophysectomized rats receiving treatment with either testosterone propionate (TP) or progesterone. After treatment with alpha-MSH for 2 weeks, increases in sebum secretion occurred in intact, castrated and hypophysectomized rats, but larger responses were found in the hypophysectomized rats that had received treatment with either TP or progesterone, suggesting that alpha-MSH acts synergistically with TP and progesterone to stimulate sebum secretion. Alpha-Melanocyte-stimulating hormone also increased preputial gland weight in intact rats, but there was no response after castration and only a small response after hypophysectomy. However, when the hypophysectomized rats received simultaneous treatment with either TP or progesterone, alpha-MSH increased preputial gland weight. It is suggested that alpha-MSH acts directly on the sebaceous glands to stimulate lipogenesis and, together with steroid hormones, may have an important role in controlling sebaceous glandd function in the rat and other hairy mammals. With the evolution of hair, certain of the MSH peptides may have lost their significance as pigmentary hormones and have developed a sebotrophic function. For this reason, it might be more appropriate to refer to these peptides as the 'sebotrophins'.

Cimetidine, 1g orally per day, partially inhibited sebum excretion in patients with acne. Whether this was the result of H2-receptor blockade or an antiandrogen action is unknown.

The sebum excretion rate (SER) was measured in fifty-five patients with rosacea and 126 control subjects. The mean SER in the patients with rosacea was not increased, nor was there any correlation between SER and severity of rosacea. Our data suggest that seborrhoea plays no part in the pathogenesis of rosacea.

This review describes the various types of sebaceous glands, their locations, and where possible their different functions. All sebaceous glands are similar in structure and secrete sebum by a holocrine process. However, the nature of this secretion and the regulation of the secretory process seem to differ among the various types of glands. Methods for measuring sebum secretion and assessing sebaceous gland activity are also described. The area of major interest during the last 20 years has undoubtedly been the mechanisms that control sebaceous gland function. Most studies have focused on the endocrine control and in particular on the role of androgens and pituitary hormones, although evidence suggests that nonendocrine factors may also be important. However, many questions remain and during the next few years attention will certainly be given to the role of retinoids and their mode of action in the treatment of acne.

Sebum excretion rates from forehead skin were measured serially during and after pregnancy in 10 normal women. Only minor fluctuations occurred during the middle and last trimesters of pregnancy, but there was a pronounced decrease in the postpartum period. Probably a powerful sebotrophic factor is present in pregnancy, but its nature is conjectural.

The rate of sebum excretion from the forehead skin of patients with early breast cancer was found to be just significantly higher than in age-matched control women. This may indicate that some breast cancer patients have an increase in circulating or tissue-bound sebotrophic hormones, or a decrease in their inhibitors.

The sebum excretion rate (S.E.R.) was measured in 20 patients with acromegaly. Eleven were untreated at the time of the measurement and nine had previously undergone surgical hypophysectomy or had received pituitary irradiation by yttrium-90 or radiotherapy. In five patients the S.E.R. was measured before and after such treatment. The mean S.E.R. in the untreated acromegalics was much greater than in a normal population and decreased significantly after successful pituitary ablation. No significant decrease in mean S.E.R. occurred in the group of patients with a poor clinical response to ablation. The correlations between S.E.R. and log serum growth hormone, plasma 11-hydroxycorticosteroid levels, and heel-pad thickness were significant, but there was no significant correlation between S.E.R. and serum protein-bound iodine levels. This suggests that the changes in S.E.R. were due to pituitary ablation but could not necessarily be attributed solely to changes in growth hormone, thyroid-stimulating hormone, or adrenocorticotrophic hormone. The association between the clinical state of the acromegaly and the S.E.R. was better than the association between acromegaly and serum growth hormone. We conclude that the S.E.R. is a useful addition to the clinical and endocrinological data used in assessing acromegaly.