Erythema infectiosum (fifth disease). Erythema infectiosum is a mild childhood disease that is caused by human parvovirus B19. This condition develops after a mean incubation period of 14 days. There are few if any prodromal symptoms. The rash evolves in three clinical stages. The first stage is characterized by the abrupt appearance of a bright-red malar blush. The appearance is so startling that it has been given the suggestive description of “slapped cheeks”. During the second stage, the facial rash begins to fade, and a maculopapular, urticarial, or morbilliform exanthem develops on the extremities and trunk. Pruritus may be present.
Phytophotodermatitis. In addition to perfumes, a number of plants, grasses, fruits, and vegetables contain psoralen as a photosensitizer. The child who helps mother or father slice limes before a trip to the park may develop an identical eruption on the hands. Celery and parsley may present similar problems. It is important to recognize this entity since some affected infants and children have been mistakenly thought to have bruising from child abuse.
Allergic contact dermatitis (reaction to temporary tattoo). Contact allergy to temporary tattoos has become an increasingly common phenomenon. In most cases, the tattoo material does not contain pure henna, but is a mixture of brown henna with paraphenylenediamine (PPD) called black henna. The patient is allergic to PPD in the tatto. In fact, the concentration of PPD in black henna is higher than that seen in commercial hair dyes. After resolution of the eczematous skin eruption, postinflammatory hyperpigmentation may persist for a considerable period of time.