The patch test can be used to identify the offending substance that has caused the rash. A number of patches containing allergenic substances, as well as any products that the patient might suspect, are applied to the back and left there for 48 hours.
The patches are then removed and any inflammatory reactions noted. The reactions might vary from mild to extreme.
This patient developed inflammation and blistering under the dressing applied to his arm.
Colophony is used to help many dressings to 'stick' to the skin. It is also used in gels for the treatment of warts, cosmetics, soaps and shampoos, wood polishes, resin for stringed instruments and varnishes. It is present in the cement and impression pastes used by dentists.
The patient should be advised to inspect the labels of products carefully, avoiding anything suspect and looking for suitable alternatives. The allergy will remain for a lifetime.
This patient developed an eczematous rash at the site of contact with the nickel stud in her jeans. She was advised to cover the back of the stud with fabric to prevent skin contact.
Nickel sensitivity is a very common problem and women are particularly affected.
Nickel is found in most metal and metal-plated objects, including kitchen utensils, scissors, costume jewellery, watches, drawer handles and coins.
Covering utensils and handles with a polyurethane clear varnish can help.
BLACK RUBBER ADDITIVES
A patch test confirmed that this patient's dermatitis was caused by the presence of N-Isopropyl-N-phenyl-4-phenylenediamine in the black rubber insoles that he was wearing in his shoes.
Patients with this allergy should also avoid rubber gloves, elasticated underwear, rubber boots, car tyres, and some protective masks such as those used by divers.
LANOLIN (WOOL ALCOHOLS)
This patient had been applying cream to her legs to alleviate the dryness of her skin. She developed an eczematous rash which blistered and broke down. Patch testing confirmed lanolin to be the allergen.
Lanolin derives from the sebum of sheep and is a common ingredient of many ointments, creams, lotions and soaps. The list of topical agents containing lanolin includes some steroid preparations. It is also found in furniture polish, leather, paper, printing ink, shoe polishes and some textile finishes.
Patients should be advised to check all product labels.
This patient developed a severe scaling, eczematous rash on her face together with a secondary infection of the area following the use of a depilatory cream. It settled with a course of flucloxacillin and topical fusidic acid with betamethasone. The patient was advised not to use the product again, or anything else that might contain the same ingredients.
Chemical depilators are available as creams, gels, lotions or aerosols, and they might contain sodium or calcium thioglycolate. They cause hydrolysis and disruption of the disulphide bonds of hair keratin, so the hair breaks and separates from the skin.
Users are warned to perform a patch test before using such products.
This patient was prescribed a topical steroid containing neomycin for an eczematous area on the leg.
Initially the rash settled, but then returned despite continued application. The diagnosis of neomycin allergy was confirmed by patch testing and the patient was warned not to use anything containing neomycin in the future.
Topical neomycin is frequently prescribed for the treatment of inflamed and infected lesions of the skin, eyes and external ear.
Contact with the juices of certain plants can lead to an allergic dermatitis. In the UK the plants most commonly associated are primula, which contain a quinine (primin) on the hairs on the leaves, stems and flowers.
Other plants that cause sensitivity reactions are chrysanthemums, which contain sesquiterpene lactones, and the bulbs of tulip, garlic and onion.
Typically the papulovesicular or vesicobullous allergic reaction takes on a streaky, linear pattern.
The bulb dermatitis usually presents as a dry eczema on the fingertips. Topical steroids should settle the rash.