Contacts with a variety of other chemicals have been reported uncommonly  as a  cause  of industrial acne. They include DDT, asbestos, pitch, creosote, crude tar and heavy water distillate. Comedo naevus Comedo  naevus (naevus comedonicus) is  an unusual naevoid abnormality, usually of the hair follicle, with a wide range of clinical features.

  Numerous investigators, depending upon  whether they have emphasized the clinical or microscopic features, or both, have coined various descriptive names for  this naevoid condition . Such names included comedo naevus, naevus comedonicus, naevus follicularis,  naevus  keratosis, naevus  acneiformis, naevus unilateralis comedonicus whilst Montpelier decided that zoniform naevus best described the disease. Beerman and Homan supported the view that the comedo naevus is a developmental defect of the hair follicle and that the sebaceous glands may be normal, hypoplastic or  absent, but never hypertrophic. In one patient with a palmar naevus, the lesions  arose  from the sweat ducts.

  Clinically,  comedo  naevus  is  divisible  into  two types: in one type comedones alone are present and in the second type inflammatory papules  also exist.  The lesions are  more often localized, unilatereal and linear but there  have been six cases reported  of bilateral comedo naevus. One case is reported  affecting much of the left side of the body.

  The lesions are normally present on  the scalp, face, neck, trunk and arms, and occasionally at other sites, such  as the  penis. Although the lesions may be present at  birth they can develop much  later in  life. Symptoms  are usually of a cosmetic nature; only rarely do  chronic inflammatory lesions arise and this  may produce residual scarring. Trichilemmal cysts have also been reported to arise in the naevus.

  There have been several reports of comedo naevus associated with other lesions, e.g. cataract, linear basal cell naevus and epidermolytic  hyperkeratoses. Therapy is often unrewarding, although topical retinoic acid may be of value. Naevus sebaceous of Jadassohn This not uncommon naevus arises during the first few months of life  and may be  occasionally  present at birth. It often affects the scalp and begins as an area of alopecia, this being replaced by a pinkish fleshy swelling ; the lesions consist of a mixture of relatively normal-appearing epidermis, dermis, sweat glands and sebaceous glands.

  Mehregan  and  Pinkus  reviewed  150  cases  and pointed out  that the lesions  progress through three distinct stages.100 In stage 1, from birth to puberty, the lesion  is small, hairless and may even  regress. At puberty, stage 2, the sebaceous glands enlarge and the epidermis becomes verrucous, pitted and unslightly. Stage 3 is the development of neoplastic  change in up to 25 per cent of cases; basal cell carcinoma is the most common tumour,  although squamous  cell carcinoma and trichoepithelioma  may occasionally arise. It has been suggested that naevus sebaceous is a spectrum of an organoid naevi and maybe certain subgroups have different complications.99 If possible  excision is advisable. Functional naevi of the sebaceous gland This  group includes  very uncommon conditions in which there are increased (or decreased) functional and structural  abnormalities   predominantly   of   the sebaceous element. 56    ACNE Unilateral acne Figure 3.66 shows a patient with  virtually unilateral acne on one side of the trunk.101 Investigations showed increased sebaceous lipogenesis on that side. It could be argued that the abnormal side was  the left side, which failed to  develop acne.