Allergic and autoimmune rashes
Acne, psoriasis and eczema are considered seperately. Here are some of the other common allergic and autoimmune rashes.
Contact dermatititis
Can be caused by anything: plants, cosmetics, dyes, elastic, nickel. Symptoms: redness, vesicles or papules, crusting and scaling, itching. If things become chronic, you can get fissures, hyperpigmentation and pain and burning. In terms of treatment, avoiding the irritant is the key treatment. Emollients can be used where there is no skin breach. In more severe forms topical steroids and oral antihistamines can be used.
Drug reactions
Lichen planus
Probably an immune reaction (nobody's sure). Itchy, 2-5mm, red/violet, shiny, flat-topped papule with white streaks (called Wickham's striae). Acute onset and lesions may ulcerate. The lesions most commonly occur in the flexor areas and some others: front of wrists, flexor aspect of forearm, genitals, lumbar region, ankles, shins. They follow lines of trauma. Mucous membranes can be affected. Nails and scalp can be involved (10%).
Often resolves spontaneously. Symptomatic treatment for itching using topical steroids and sedating antihistamines. In extensive cases, 30mg prednisolone od 10 days can be used.