Investigation of an outbreak of photodermatitis confined to one shop in a large factory.

Out of 106 men employed in a foundry attached to a large factory, 29 men developed a photosensitization dermatitis over the period of three months. Three men out of 1,700 employed in the remainder of the works developed a similar eruption, but no common factor was apparent. Owing to the very high incidence in the foundry, a sensitizer associated with the process was suspected and it seemed likely that it would prove to be an atmospheric contaminant. Many chemical investigations and skin tests were carried out without positive result, though much interesting information regarding combustion products of various materials was obtained. Some of the men were referred to dermatological clinics in three neighbouring hospitals. In one of these clinics, a similarity was noticed between six cases recently seen there. This suggested that the sensitizer was not confined to the foundry or to the factory. The cause was eventually traced to an additive (tetrachlorsalicylanilide) in a popular brand of toilet soap, and it was evident that the photosensitivity in varying degrees of severity was widespread over the Home Counties, if not much of the country. It had not hitherto been recognized, as mild cases had required little or no treatment, and severe cases were widely disseminated. It is probable that, had it not been for the very high incidence in the foundry, the eruption would have remained unrecognized for much longer. The high incidence in the foundry is attributed to the frequency with which the men washed there, and possibly to some local aggravating factor not yet discovered.