Itching

Also known as pruritus, itching is a common complaint with a multitude of causes.  It may or may not be accompanied by other symptoms such as rash. Most causes of itching are benign. Almost everybody will experience itching at some point in their lives and it will mostly be a minor irritation. In some cases, it can be long lasting or disruptive affecting our daily lives & our sleep.

Itching may run in conjunction with other symptoms depending on the cause.

While scratching often provides temporary relief from the itch, it can damage the skin, leading to wounds which can become infected.

Itching can be defined as localised or generalised and can be split into several categories depending on the cause. This may include;

• Parasitic
• Allergic
• Medical
• Dermatologic
• Certain medications

It is impossible to cover all causes of itching, but below is a list of the more common ones;

Parasitic

Head Lice:

Head lice (Pediculus humanus capitis)  are small, wingless parasites that live on & spend their entire life cycle on the human scalp, feeding off blood. They are most commonly found in school aged children although can infest anybody. Girls appear to get head lice more often than boys.

Pubic lice (crabs):

Pubic lice (pediculosis/crabs/pubic crabs) are are small, wingless parasites that live in public hair around the genitals & perianal regions, feeding off the blood of their host. They can also be found on other areas of the body that has thick hair such as beard, under arms, eyebrows & eyelashes.

The most common mode of transmission is close physical contact, such as during sexual activity. Pubic lice can also be spread via shared towels, clothing, bedding etc.

Body lice:

Unlike head and public lice which live on us, body lice live on clothing. But like head and public lice, body lice feed on our blood which leads to itching.

Scabies:

Scabies is a highly contagious, intensely itchy skin disease caused by a tiny mite called the Sarcoptes scabiei or human itch mite.

Sarcoptes scabiei spend their entire life cycle on humans. The fertilised female  burrows into the person's skin, forming small tunnels where she lays her eggs. These hatch into six legged larvae approximately 4 days later. After feeding, the skin is shed and the eight-legged, sexually mature nymph appears. Following several skin molts, the mature adult male is formed.

Chiggers:

Trombiculid mites (also known as harvest mites & red bugs)  are tiny vivid red-orange coloured mites that are closely related to ticks.

Only the larval form (known as chiggers) are parasitic to humans. Once on the host, they pierce the skin with specialized mouthparts & inject saliva containing digestive enzymes to break down the skin cells on which it feeds. The surrounding tissue eventually walls off the area, creating a straw like funnel (called a stylostome). This protects surrounding tissue but gives the chigger a funnel in which to continue to inject saliva & keep feeding. The larvae are able to remain on the skin for up to four days during feeding, although they are easily brushed or fall off before they are finished feeding. Chiggers can also attack other vertebrates, including cats and dogs.

Ringworm:

Ringworm is a common infectious skin infection seen in many species of mammal, including cats, dogs & humans. Contrary to the name, ringworm is caused by a microscopic group of parasitic fungal organisms known as dermatophytes (which means plants that life on the skin). Ringworm invades the dead, outer layers of the skin, nails (or claws), and hair. The fungus thrives best in areas that are warm & moist. There are several types of ringworm which can cause itching including;

• Tinea corporis - Ringworm of the body in general.

• Tinea capitis - Ringworm of the scalp. This is most often seen in children.

• Tinea cruris (also known as Jock Itch) - Ringworm of the groin.

• Tinea barbae - Ringworm of the bearded area of the face and neck.

• Tinea faciei - Ringworm of the face (excluding the bearded areas)

• Tinea manus - Ringworm of the palms and fingers.

• Tinea pedis (also known as Athlete's Foot) - Fungus of the foot.

Pinworms:

Also known as threadworms, pinworms (Enterobius vermicularis)  are a small, threadlike worm of the colon and rectum. Pinworms are most common in school aged children, although any individual can become infected with pinworms.  Humans are the only natural host for pinworms. They are the most common parasitic worm to infect humans. They are a common cause of anal itching (pruritus ani).

Other causes of anal itching include certain foods, fungal or bacterial infections, hemorrhoids, poor hygiene,  genital warts, genital herpes.

Insect bite:

Insect bites and stings can cause localised itching and swelling. Common insect bites include; mosquito, ants, bedbugs, fleas and flies. Typically, along with itching, bug bites also have the following symptoms; localised pain, redness, small, raised spot.

Allergic

Contact, atopic & allergic dermatitis are all caused by exposure to allergens such as chemicals, soaps, certain foods, plants (nettles, poison ivy etc.) or pollens (hayfever) and can lead to itching.

Allergic reactions vary from mild itching to life threatening anaphylaxis.

Medical

Many medical conditions include symptoms of itching. Some include; liver disease, kidney failure, iron deficiency, thyroid disorders, certain cancers.

Dermatologic

Eczema:

Eczema is an itchy skin disorder caused by an inflammation of the skin that affects people of all ages, but commonly appears in early childhood. Most children will grow out of eczema by their teenage years.  It is more often seen in families with a history of allergies, asthma & hay fever.

Psoriasis:

Psoriasis is a chronic, recurring autoimmune disease characterized by red, thickened patches on the skin, often with silvery scales. It is the result of overproduction of the skin cells. Usually, cell turnover occurs roughly every 28 days, but in the case of psoriasis, this happens every few days instead, resulting in a thickening of the skin in the affected area.

Around 2% of the Western population are affected by psoriasis. Men & women are both equally affected. It is an inherited condition (runs in families) that is not contagious to others.

Dandruff:

Dandruff (also known as Pityriasis capitis) is a common condition caused by an excessive shedding of the dead skin cells (keratinocytes) of the scalp. The epidermis is the outermost layer, consisting of skin cells. These cells are continually being shed & renewed approximately every month, however cell turnover is much more frequent in people with  dandruff.

Dry skin:

Also known as xerosis, dry skin can happen to anybody, but it is more common in older people when their sebaceous glands produce less sebum (oil), which lubricates & protects the skin. Dry, windy & cool weather also see an increase in dry skin.

Sunburn:

Sunburn is a burn to the skin & is a result of too much exposure to the sun's harmful UV rays. It can occur with just a few minutes of exposure to the sun & or even on cloudy days. Sunburn can also occur with the use of sun beds.

Tinea versicolour:

Also known as pityriasis versicolor, tinea versicolour is a common fungal infection of the skin characterised by discoloured patches of skin on the torso. Tinea versicolour is caused by a yeast of the genus Malassezi. These fungi are found on healthy skin in small numbers, however in some people, the fungus begins to overgrow, leading to patches of discoloured skin.

Other common causes of itching include;

Chicken pox, scab healing, razor burn, ingrown hair, folliculitis, vaginal infection (bacterial or fungal), pregnancy, worms.