Scabies signs and symptoms include:

• Itching, often severe and usually worse at night
• Thin, irregular burrow tracks made up of tiny blisters or bumps on your skin

The burrows or tracks typically appear in folds of skin. Though almost any part of the body may be involved, in adults and older children scabies is most often found:

• Between the fingers
• In the armpits
• Around the waist
• Along the insides of the wrists
• On the inner elbows
• On the soles of the feet
• Around the breasts
• Around the male genital area
• On the buttocks
• On the knees

In infants and young children, common sites of infestation usually include the:

• Scalp
• Palms of the hands
• Soles of the feet

If you've had scabies before, signs and symptoms may develop within a few days of exposure. If you've never had scabies, it can take as long as six weeks for signs and symptoms to begin. You can still spread scabies even if you don't have any signs or symptoms yet.

The eight-legged mite that causes scabies in humans is microscopic. The female mite burrows just beneath your skin and makes a tunnel where it deposits eggs.

The eggs hatch, and the mite larvae work their way to the surface of your skin, where they mature and can spread to other areas of your skin or to the skin of other people. The itching of scabies results from your body's allergic reaction to the mites, their eggs and their waste.

Close physical contact and, less often, the sharing of clothing or bedding with an infected person can spread the mites.

Animals and humans all are affected by their own distinct species of mites. Each species prefers one specific type of host and doesn't live long away from that preferred host.

Humans may have a temporary skin reaction from contact with the animal scabies mite. But people are unlikely to develop full-blown scabies from this source, as they might from contact with the human scabies mite.

Vigorous scratching can break your skin and allow a secondary bacterial infection, such as impetigo, to occur. Impetigo is a superficial infection of the skin that's caused most often by staph (staphylococci) bacteria or occasionally by strep (streptococci) bacteria.

A more severe form of scabies, called crusted scabies, may affect certain high-risk groups, including:

• People with chronic health conditions that weaken the immune system, such as HIV or chronic leukemia
• People who are very ill, such as people in hospitals or nursing facilities
• Older people in nursing homes

Crusted scabies, also called Norwegian scabies, tends to make skin crusty and scaly, and affects large areas of the body. It's very contagious and can be hard to treat.

Normally, someone with scabies has about 10 to 15 mites. In contrast, someone with crusted scabies may be infested with millions of mites.