Köbnerizing occupational contact allergy to thiuram in a farmer with psoriasis.

are important factors in the elicitation of contact dermatitis. Our current data show that patients with a history of using temporary black henna tattoos are often highly sensitized to PPD after exposure to such high concentrations and require only very low concentrations of PPD for elicitation of an allergic response. As the current practice of using PPD 1% pet. often results in unacceptably strong blistering reactions, we propose patch testing with PPD 0.01% pet., which can elicit a sufficiently positive reaction in a highly sensitized individual. If this is negative at the 1st reading, the concentration of PPD can then be stepped up to 0.1%, or even 1% to ensure that an allergic contact dermatitis from PPD is not missed.