There is uncertainty about the rates of absorption and the clinical sequelae for chloracnegens and for obvious reasons experimental studies in humans are lacking.

  The most likely route of absorption is through the skin; ingestion and/or inhalation are relatively uncommon. Following topical absorption there is the tendency for chloracne to be more severe than systemic changes. Conversely, the  only incident where absorption was known to  be solely by ingestion led to 18 per cent of over 1,000 cases developing signs of systemic poisoning without chloracne being present.

  Until the 1980s investigations were hampered by lack of analytical methods sufficiently sensitive to study chloracnegens in tissues. In one study very sensitive gas chromatography and mass  spectrometry  techniques failed to demonstrate the  presence of dioxin in  comedones and cysts. (The samples were, however, taken 5-11 months after exposure.) Nevertheless, the patients had active disease  with many comedones. Analysis of their  skin lipids showed  them  to  be exclusively of epidermal origin.83 This fits with the histological picture of squamous metaplasia of the cells lining the ducts and of the  sebaceous gland. 

The sensitivity of the follicular canal to chloracnegens is amply demonstrated in rabbit  ears in  concentrations of 0.001-0.005 per cent. Management Longterm follow-up of such patients is necessary and litigation is  a  common event. Retinoic acid topically plus physical removal of the comedones  with  a  comedone extractor, along with cautery of the cysts, are usually of help. Oil acne Fiddler's neck Although working with mineral  oil can predispose to acne,84 oil acne is now very uncommon. Investigations have shown that oil acne may result  from  insoluble cutting  oils causing mechanical obstruction  of the pilosebaceous duct. Only occasionally do frank inflammatory lesions arise, these being in the form of papules and pustules;  furunculosis and  scarring may result. This type of acne can occur as early as six weeks after exposure and commonly affects those areas of the skin in contact with  the oil,  in particular  the thighs  and lower arms. In the past thirty years, oil acne has been seen much less frequently in the dermatolgy clinics, as a result of an improvement in working conditions.

  Crude petroleum in oilfield  and refinery works and vegetable oils used as cosmetics in India85 are  known to be comedogenic. Fiddler's neck   is  a  condition affecting violin  and viola players.  Although  well  known to musicians, it is not well-recognized by dermatologists. Clinically, the lesions usually consist of a localized area of lichenification on the neck - just below the angle of the jaw.86 Pigmentation, erythema and inflammatory papules, or  pustules,  are frequently present  but nodules, cysts and scarring occur much less often. The aetiology of the  skin changes is probably due to  a combination of factors - friction giving rise to lichenification, while local pressure, shearing stress and occlusion may play a part in producing the acne-like changes. Treatment with retinoic acid may help.