A halo nevus 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 infest and cause 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. 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.

A hemangioma (or angioma) is a small non-cancerous overgrowth of blood vessels in the skin. They occur in up to 10% of infants and can occur in adults as well. The Strawberry hemangioma, or Capillary Naevus, is more common in premature babies. The hemangioma 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 hemangiomas bleed or ulcerate.

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) 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. Susceptible contacts may develop chickenpox from exposure to the infected patient

Hidradentis Supporative is a chronic pustular scarring 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 ocassionally surgery to remove affected area.

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, and is often genetic in origin. 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 are also know as Urticaria and refers to a group of disorders in which wealing occurs in the skin. The weals can be a few millimeters or several centimeters diameter, colored white or red, often surrounded by a red flare, and frequently itchy. Each weal may last a few minutes or several hours, and may change shape. Weals may be round, or form rings, a map-like pattern, or giant patches. The surface weals may be accompanied by deeper swelling of eyelids, lips, hands and elsewhere, called angioedema. Angioedema may occur without urticarial weals. The weals and swellings occur because of the release of chemicals, particularly histamine, into the tissues. This causes small blood vessels to leak, allowing fluid to accumulate in the skin. People often associate acute urticaria with an allergic reaction. Typically, medicines such as antibiotics, or food, including even tiny amounts of fish, eggs, nuts or chocolate, are responsible. It depends on previous exposure to the material, and the development of an immune reaction to it.

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. 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 is the name given to excessive sweating. Hyperhidrosis may affect the entire body, or it may be localized to the armpits, palms or soles. Hyperhidrosis may occur in childhood or start later in life. Other family members may be similarly affected. 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.

Ichthyoses refers to a group of mainly hereditary type of skin diseases where the skin resembles reptile scales. Occasionally, this condition occurs in patients with severe underlying disease such as cancer or tuberculosis.

Impetigo is a skin infection caused by bacteria. It is often called "school sores" because it affects children and is quite contagious. Streptococcus pyogenes and/or Staphylococcus aureus are the microorganisms responsible for impetigo. Impetigo most often occurs on exposed areas such as the hands and face. It presents with pustules and crusted oozing patches which grow larger day by day. Impetigo may be caught from someone else with impetigo or boils, or appear "out of the blue". It often starts at the site of a minor skin injury such as a graze, an insect bite, or scratched eczema.

After a bite there is usually a hive like reation where the skin becomes red, swollen, and itchy covering an area of less than 1 cm. This reaction may last for up to 2 weeks. Occasionally one or two bites may trigger dozens of lesions to come out all resembling the intial bite called papular urticaria. (see papular uticaria)

Intertrigo is the word used to describe a yeast and bacterial infection involving body folds. Affected skin is reddened and uncomfortable. Intertrigo is particularly common in those who are overweight. Body folds (flexures) are prone to inflammatory rashes because of: Relatively high skin temperature; moisture from sweating; and friction from movement of adjacent skin. Bacteria and yeasts, which are normally resident on the skin, multiply in such environments and result in an irritated and macerated area of skin.

Occasionally scars enlarge spontaneously to form firm, smooth, hard growths called keloids that may be uncomfortable or itchy, and may grow much larger than the original wound. If there is excessive tension on a healing wound, the healing area can thicken more than usual. This is known as a hypertrophic scar.

A keratoacanthoma is a variant of squamous cell carcinoma, which looks like a little volcano with a "core" in it. A keratoacanthoma (KA) often starts at the site of a minor injury to the skin, which has previously been damaged by the sun. At first it may appear as a small pimple or boil and may be squeezed but is found to have a solid core. It then grows rapidly and by the time it is brought to the attention of your doctor may be up to 2 cm in diameter.

There are numerous tiny rough spots in the affected area. Each one is a horny plug, sometimes rather red but only rarely itchy and never sore. Keratosis Pilaris is a very common finding on the outer aspect of the upper arms of teenagers. It may occur in babies where it tends to be most obvious on the cheeks. It may remain for years but generally becomes less obvious in adult life; keratosis pilaris is uncommon in elderly people. Keratosis pilaris tends to be more severe during the winter months or other times of low humidity when skin dries out. It occurs because as the skin renews itself, old skin cells in the hair follicles get stuck, forming a scaly plug.

For reasons not yet clearly understood, some individuals can become allergic to certain constituents of the latex molecule. Once allergic, you may remain sensitive for the rest of your life. The common reactions of latex sensitive individuals exposed to latex are contact urticaria, dermatitis and asthma. Contact urticaria usually presents with itching and swelling of the skin at the site of contact with latex. This may, for example, be a hand from wearing gloves, genitals from contact with condoms, etc. The symptoms usually start within 5 - 15 minutes after coming into contact with the latex article, although it can be delayed for several hours. Symptoms can continue for a variable period, from several hours to days after the latex contact has ceased. Contact dermatitis from latex may take several days to appear. It presents with an itchy, scaly rash, although there may be small blisters if the reaction is acute. The rash will usually last several days to weeks but if exposure to latex continues, the rash will last longer. Contact dermatitis is not generally caused by sensitivity to latex protein but rather to the chemicals used in the manufacture of the latex product, including antioxidants and rubber accelerators e.g. thiuram, carbamates, MBT, etc. Immediate-type hypersensitivity requires previous sensitizations and is the most potentially dangerous reaction to latex. Clinical presentations vary but may include contact urticaria, coryza, conjunctivitis, stinging or burning, asthma, and, with mucosal or parenteral exposure, anaphylaxis. A common cause for the asthmatic reaction is powdered gloves. The starch powder picks up the latex proteins and when the gloves are removed the powders can then be inhaled or come into contact with the skin on the face where it can cause an allergic reaction.

These represent areas of permanent sun damage that pose no threat to the patient. They are areas of the skin in which the pigment producing cells (melanocytes) are damaged and typically overproduced pigment leading to so called "liver spots" or "age spots" on the hands face and chest. These can be successfully removed with a laser. Sometimes the opposite may occur and the melanocytes underproduce pigment resulting in a white spots.

Lentigo Maligna is a type of melanoma that arises on the face and can mimic a lentigo early in its course. This type of lesion makes it imperative that only a Dermatologist is qualified in the laser removal of pigmented (brown) spots.

Lichen planus is an inflammatory skin disease that is characterized by shiny violet colored very itchy bumps. Commonly affected areas include the wrists, ankles, penis and inside the mouth. The nails can also be affected. There is occasionally an association with hepatitis. Treatments include steroids, retnoids and light.

Lichen simplex chronicus (neurodermatitis) is a common skin dermatitis that results from repeated rubbing or scratching of the skin. The stimulus to scratch may be unrecognized, perhaps a mosquito bite, stress, or simply a nervous habit. The result is a very itchy patch of skin, often located on the nape of the neck, scalp, shoulder, wrist, ankle, or genitals. The affected skin is thickened, often appearing as a group of small firm papules (bumps). The skin markings are more visible, and the hairs are often broken-off. The color may be darker or sometimes paler than the surrounding skin. Lichen simplex tends to be very persistent, and readily recurs despite often initially effective treatment.

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