In humans, a scabies infestation looks like a series of irregular thin tracks on the skin made up of tiny bumps or blisters, Mayo Clinic says. In adults, these tend to be concentrated in folds of skin, such as in armpits, in the inner elbow, between fingers, in the male genital area or around breasts. In infants and young children, scabies tracks tend to appear on the scalp, neck, palms of the hands, face or soles of the feet.
The tracks caused by scabies tend to be severely itchy, and this sensation is often worse at night, explains Mayo Clinic. This can lead to secondary infections by bacteria when a person with scabies scratches too vigorously and breaks the skin. Scabies itself is caused by a mite, a microscopic animal with eight legs. This animal burrows through the skin and leaves the telltale tracks. They lay their eggs in the tunnels they leave behind, and newly hatched mites emerge from the skin to spread to other people. The itching is caused by an allergic reaction to the mites, along with their eggs and wastes.
Scabies is very contagious and spreads by contact with other people, Mayo Clinic says. The first time a person is infested, symptoms may not appear for up to six weeks. Symptoms appear faster in any subsequent infestations.