Human scabies is caused by female scabies mites burrowing in the upper layer of human skin, and then laying eggs. Those eggs eventually hatch, and the process repeats itself, quickly multiplying into an infestation. The most common scabies symptoms include itching and skin rash, both associated with an allergic reaction to the mites and their feces. The itching associated with scabies is often severe and usually gets worse at night [source: Mayo Clinic]. These symptoms can affect nearly any part of the body, but are most often found on the wrist, elbow, armpit, penis, nipple, waist, buttocks and between the fingers [source: Centers for Disease Control and Prevention].
In addition to the itching and skin rash, some sufferers of scabies will develop scabies rash, which is a pimple-like breakout across the infected areas of the body. Occasionally, a person will be able to see the burrows created by female scabies mites digging underneath the skin. These appear as tiny raised and crooked lines across the skin's surface. Although uncommon, scratching the scabies can also lead to skin sores, which could eventually become infected with bacteria commonly found on the skin [source: Centers for Disease Control and Prevention].
Scabies symptoms don't develop for several weeks after infestation, and this delay often causes the symptoms to be more severe by the time they are treated.
Although they aren't as common, crusted scabies (also known as Norwegian scabies) are a severe form of the disease identified by thick crusts over the skin. These crusts contain high concentrations of mites. People who have crusted scabies may not have traditional symptoms of the disease -- itching or scabies rash. Crusted scabies usually occur in people who have a weakened immune system or a neurological problem. Additionally, the disease may occur in people who physically cannot itch (people with spinal cord injuries or paralysis to name a few) and therefore will not develop the traditional scabies symptoms. People suffering from this condition can be infested with as many as two million mites, and as a result, they are extremely contagious. They should seek medical care immediately [source: Centers for Disease Control and Prevention].
In the next section, you'll read about the different ways that humans contract scabies.