The main symptoms of scabies are:

• intense itching that is worse at night
• skin rash in the areas of the body where mites have burrowed

These symptoms are described in more detail below.

Intense itching

The main symptom of scabies is intense itching that is worse at night when the skin temperature is warmer. The itching may take between four to six weeks to develop because this is the length of time that it takes for the body to react to the absorption of mite droppings into the skin cells.

If you have had a previous infection, the symptoms will begin to show within one to two days. This is because your immune system will have learnt to react to a scabies infection.

Skin rash

The skin rash that is associated with a scabies infection is made up of tiny red insect bites or spots. If you scratch the rash, you may also develop crusty sores.

Burrow marks can be found anywhere on the body but, in adults, they often appear in the following areas:

• the folds of skin between the fingers and toes
• the wrists
• the elbows
• around breast nipples (in women)
• around the male genital area

The rash can also sometimes occur in the following areas:

• the underarm area (axillae) 
• around the waist
• the inside of the elbow
• the lower buttocks
• the lower legs
• the soles of the feet
• the knees
• the shoulder blades
• female genital area
• the nipples
• the groin
• around the ankles

Elderly people, young children and those with a low immune system (immunocompromised) may also develop a rash on their head and neck.

In infants and young children, burrow marks tend to appear at different locations on their body, including the:

• face
• head
• neck
• scalp
• palms of the hands
• soles of the feet

The scabies mites also leave small red blotches and silver coloured lines on the skin. These marks are caused by the mites burrowing into the skin.

Blisters and pustules (small blisters that contain pus) on the soles of the feet and palms are also a common characteristic of scabies in infants.

The scabies mite life cycle

Scabies is a skin condition that is caused by the human parasite Sarcoptes scabiei. An infestation (the presence of animal parasites inside the body) starts when a female mite burrows into your skin.

Male mites move between different burrow sites looking to mate with an unfertilised female. After mating has taken place, the male mite dies and the female begins to lay eggs. The eggs hatch around three or four days later.

After the eggs have hatched, the young mites move to the surface of the skin where they mature into adults. It takes between 10 to 15 days for the mites to mature. The male mites stay on the surface of the skin, and the female mites burrow back into the skin in order to create a new burrow. The life cycle is then repeated.

Without effective treatment, the life cycle of the scabies mite can continue indefinitely. Scabies mites are resistant to soap and hot water and they cannot be scrubbed out of the skin.

The exact cause of the intense itchiness that is associated with scabies is unknown, but most experts believe that the it is caused by the immune system reacting to the mites and their saliva, eggs and faeces (stools).

How scabies is transmitted

Scabies mites cannot fly or jump, so they can only move from one human body to another if two people have direct and prolonged physical contact. For example, scabies mites can be transmitted by:

• holding hands with someone who is infected for a prolonged period of time
• having sex with someone who is infected
• sharing a bed, towels or clothes (although this is rare)

Transmission through brief and limited physical contact, such as shaking hands or hugging someone, is unlikely.

Scabies mites can survive outside the human body for between 24 to 36 hours, so it is possible to become infected by coming into contact with contaminated clothes or bed linen. However, this is a far less common way of acquiring the condition.

Scabies infestations can spread quickly because people are usually unaware that they have the condition until two to three weeks after the initial infection has occurred. There is an increased risk of catching scabies in confined environments, such as schools and nursing homes, where people are in close proximity to one another.

People often regard scabies as a condition that is caused by poor personal hygiene and living conditions. However, there is no evidence to suggest that this is the case. Scabies can affect people from all walks of life, although certain groups have an increased risk of getting the condition.

Risk groups

Some groups of people have an increased risk of catching scabies because they are in close contact with lots of other people. Those with an increase risk include:

• children – this is due to the outbreaks of scabies that can occur at schools and nurseries
• young mothers – who are in close contact with affected children
• elderly people who live in nursing homes
• people who are sexually active

Crusted scabies

Crusted scabies (also sometimes referred to as Norwegian scabies) is a more severe form of scabies where thousands, or even millions, of scabies mites are present.

Crusted scabies can begin as scabies before developing into the more severe form following a skin reaction. Crusted scabies affects all parts of the body, including the head, neck and nails. Unlike normal scabies, the rash of crusted scabies does not itch and it can affect the scalp.

In crusted scabies, the increase in the number of mites causes the appearances of thick, warty crusts to appear on the skin. The condition is often misdiagnosed as psoriasis (a skin condition that causes red, flaky, crusty patches of skin that are covered with silvery scales).

Crusted scabies affects people who have a weakened immune system (the body’s natural defence against infection). People who may have a weakened immune system include:

• the very young
• people with brain disorders (neurological disorders, such as Parkinson’s disease)
• people with Down’s syndrome, a genetic disorder caused by an abnormality in one of the chromosomes (genetic material) that occurs when a baby is still in the womb (uterus)
• pregnant women
• elderly people
• people with a condition that affects their immune system, such as HIV or AIDs
• people who are taking steroids to treat other medical conditions
• people who are undergoing chemotherapy

Research has found that a healthy immune system seems to interrupt the reproductive cycle of the scabies mite. For example, most people who are affected by the condition will only have 5–15 mites on their body at any one time.

However, if your immune system is weakened, the number of scabies mites can increase significantly. People with crusted scabies can have thousands or millions of scabies mites in their body at any one time.

Due to the high number of scabies mites, crusted scabies is highly contagious. Even minimal physical contact with a person with crusted scabies, or with their bed linen or clothes, can lead to infection. However, transmission from someone with crusted mites will only lead to the normal type of scabies in people with a healthy immune system.

Crusted scabies can be treated by using insecticide creams, or a medicine called ivermectin, which is taken orally (by swallowing a tablet). Ivermectin kills the mites by stopping their nervous system from working.

Secondary infection

Excessive itching of the skin can break the surface of your skin, making it more vulnerable to a bacterial infection such as impetigo (a highly contagious bacterial skin infection). Antibiotics may be recommended to control a secondary infection.

See the A-Z topic about Impetigo for more information about this skin infection.

Scabies has been known to make other pre-existing skin conditions worse, such as eczema. However, if you have another skin condition, it should settle down once the scabies infection has been successfully treated.