The sting of the Portuguese man-of-war. One of the most painful effects on skin is the consequence of attack by oceanic hydrozoans known as Portuguese men-of-war, which are amazing for their size, brilliant color, and power to induce whealing. They have a small float that buoys them up and from which hang long tentacles. The wrap of these tentacles results in linear stripes, which look like whiplashes, caused not by the force of their swing but from deposition of urticariogenic and irritant substances.
Polymorphous light eruption. Patients with this condition develop papules, papulovesicles, or erythematous plaques in response to sun exposure. The lesions erupt a few hours to several days after the subject has been exposed to sunlight. Lesions are most often located on the face, upper chest, and exposed parts of the extremities. Ocular inflammation and cheilitis may also occur. Among North American and Latin American Indians, polymorphous light eruption tends to be a familial disease with childhood onset.
Ringworm is characterized by a red ring of small blisters or a red ring of scaly skin that grows outward as the infection spreads. Though children are especially susceptible to catching ringworm, it can affect adults as well.
Poison ivy, poison oak and poison sumac are plants that contain an irritating, oily sap called urushiol. Urushiol triggers an allergic reaction when it comes into contact with skin, resulting in an itchy rash, which can appear within hours of exposure or up to several days later.