Parasites

 Parasites live in or on  another organism and draw their nourishment from that organism.

Pediculosis capitis, or head lice, is the infestation of the hair and scalp with head lice.  As the parasites feed on the scalp, itching occurs and the scratching that usually results can cause an infection.  Head lice are transmitted from one person to another by contact with infested hats, combs, brushes, and other personal articles.

Pediculosis Capitis

Scabies is a highly contagious skin disease caused by a parasite called a "mite" that burrows under the skin.  Vesicles and pustules usually form on the scalp from the irritation.  Excessive itching results in scratching the infected areas and makes the condition worse.

 Mite that causes Scabies