Scabies rash has the visual characteristics of irregular thin tracks made up of lines of small bumps or blisters, states Mayo Clinic. On adults, these appear most frequently in skin folds such as armpits, around breasts, the inner elbow, between fingers and around the male genital area. The rash also appears on the soles of the feet, around the waist, the insides of the wrists, on buttocks and on shoulder blades in adults.
The tracks tend to appear in different places when infants are infested by scabies, including the face, palms of the hands, soles of the feet, scalp and neck, says Mayo Clinic. In both infants and adults, microscopic eight-legged animals known as mites cause the tracks by burrowing through the skin. They leave eggs in the tunnels they create. These, combined with the mites themselves and their wastes, cause the allergic reactions that produce the lines of bumps or blisters. These tracks can be extremely itchy, and can cause people to further damage their skin through scratching, which can lead to infection.
Scabies is extremely contagious, as newly hatched mites travel to the surface of the skin and switch hosts on contact, explains Mayo Clinic. If a doctor diagnoses a person with scabies, he generally administers treatment to everyone in regular contact with the person.