H

Halo Nevi

A halo nevi is a mole with a white ring, or halo, around it and is sometimes known as Sutton's naevus or leukoderma acquisitum centrifugum. Halo moles are not uncommon and are usually seen in children or young adults of either sex. For reasons, which are unknown, the body selects a particular mole or moles for destruction. This is presumably because the mole is recognized as being abnormal in some way. The mole in the center of a halo is rarely malignant (cancerous) although all halo moles need to be examined carefully by an appropriate medical practitioner. Sometimes halo moles are triggered by sunburn, which damages the mole and causes it to be recognized by the body as foreign.

Head Lice

Head lice have infested humans for thousands of years. Infestation with lice is quite often inappropriately considered related to poor hygiene and low socio-economic status. In fact people of all walks of life can get infested with lice and the stigma of catching lice is often borne out of ignorance. Head lice usually cause an itch and irritation in the scalp. This can take several weeks to develop after the initial infestation. Scratching can cause crusting and scaling on the scalp. Occasionally secondary bacterial infection of the scalp results in small sores on the scalp with tender glands in the neck. Dermatitis can also occur with a heavy infestation of lice. Fortunately head lice are not known to carry any diseases, which can affect humans. It is important to identify the lice (or nits) to make a correct diagnosis. Lice are around 3mm in length and can be seen moving from hair to hair. Unhatched eggs have a dark area within the shell while hatched eggs are transparent.

Hemangioma

A haemangioma (or angioma) is a small non-cancerous overgrowth of blood vessels in the skin. Ten percent of babies have them. They may occur in adults too. The Strawberry haemangioma, or Capillary Naevus, is more common in premature babies. It may appear when the baby is a few days or weeks old and rapidly grow over a few months. The eventual size varies from a tiny dot to several centimeters in diameter. Occasionally haemangiomas bleed or ulcerate, but this is rarely serious.

Herpes Simplex

Herpes simplex is one of the commonest infections of mankind throughout the world. There are two main types of herpes simplex virus (HSV); type 1, which is mainly associated with facial infections and type 2, which is mainly genital, although there is considerable, overlap. Both type 1 and type 2 herpes simplex viruses reside in a latent state in the nerves, which supply sensation to the skin. With each attack of herpes simplex the virus grows down the nerves and out into the skin or mucous membranes where it multiplies, causing the clinical lesion. After each attack it "dies back" up the nerve fiber and enters the resting state again. First attacks of type 1 infections occur mainly in infants and young children, which are usually mild or sub clinical. In crowded, undeveloped areas of the world up to 100% of children have been infected by the age of 5. In higher socioeconomic groups the incidence is lower, for example less than half of university entrants in Britain have been affected. Type 2 infections occur mainly after puberty, often transmitted sexually. The initial infection more commonly causes symptoms. The virus can be shed in saliva and genital secretions from individuals without symptoms, especially in the days and weeks following a clinical attack. The amount shed from active lesions is 100 to 1000 times greater. Spread is by direct contact with infected secretions. Minor injury helps inoculate the virus, especially into the skin. The virus can be inoculated into any body site to cause a new infection, whether or not there has been a previous infection of either type. The source of the virus may be from elsewhere on the body especially in nail biters or thumb suckers. Examples of inoculation from external sources include lesions of the hand in health-care workers, facial lesions contracted in rugby scrums, and infection of a breast-feeding mother's nipples from the infected mouth of her baby. Following the initial infection immunity develops but does not fully protect against further attacks. However where immunity is deficient, both initial and recurrent infections tend to occur more frequently and to be more pronounced.

Herpes Zoster

(Herpes Zoster) Shingles is a painful blistering rash caused by reactivation of Chicken Pox virus. Chickenpox (varicella) is the primary infection with the virus, Herpes zoster. During this widespread infection, which usually occurs in childhood, virus is "seeded" to nerve cells in the spinal cord, usually of nerves, which supply sensation to the skin. The virus remains in a resting phase in these nerve cells for years before it is reactivated and grows down the nerves to the skin to produce shingles (zoster). Shingles occurs sporadically. The annual incidence is about 3.4 per 1000. It is uncommon in childhood and the incidence increases with age. The sexes are equally affected. Shingles patients are infectious, both from virus in the lesions and in some instances the nose and throat. In susceptible contacts of shingles, chickenpox, sometimes severe, can occur.

Hidradenitis Supporative

Hidradentis Supporative is a chronic puss forming scaring disease of the apocrine (scent) glands of the armpits and groin. This starts at puberty and may last throughout life. Treatments include antibiotics, steroid injections, and sometimes surgery to remove affected area.

Hirsutism

Hirsutism is the term used for increased hair growth in women. It refers to a male pattern of hair, i.e. in the moustache and beard areas, or occurring more thickly than usual on the limbs. There may be hairs on the chest or an extension of pubic hair on to the abdomen and thighs. What is considered normal for a woman, and what is considered hirsute, depends on cultural factors and race. Hirsutism is very common. Hirsutism is nearly always genetic in origin. Female and male relatives may also have more hair than the average so hirsutism is normal in that family. Although some women with hirsutism have increased amounts of male hormone (eg. testosterone), most have normal levels. The problem in these women is that the hairs are more sensitive than normal to small amounts of hormone. The hairs grow more quickly and thicker in response to it. The increased hair growth is usually first noted in late teenage years and tends to gradually get more severe as the woman gets older. Blood tests may be arranged to make sure that the hirsutism is not due to excessive male hormone levels.

Hives

(see urticaria)

Hot tub folliculitis

hot tub folliculitis is a skin infection that is caused by bacterial infection of the hair follicle. It arises hours to a few days after bathing in inadequately disinfected warm water, such as a hot tub, Jacuzzi or swimming pool and may affect several exposed individuals. The result is an eruption of scattered small red itchy or tender bumps, some of which are pustular. They mainly occur in areas that were covered by the swimsuit.

Hyperhidrosis

Hyperhidrosis is the name given to excessive sweating. Hyperhidrosis may affect the entire body, or it may be localized to the armpits, palms or soles. Sometimes hyperhidrosis occurs in childhood. Other family members may be similarly affected. At other times it starts later on in life for unknown reasons. An increase in air temperature, exercise, fever, anxiety, or spicy food may cause sweating. Sweating usually reduces at nighttime, but can continue throughout the day.