Dermatology is the study of the skin and its associatedstructures, including the hair and nails, and of theirdiseases. It is an immense subject, embracing some2000 conditions, yet, paradoxically, some 70% of thedermatology work in the UK is caused by only ninetypes of skin disorder. Similarly, in the USA,nearly half of all visits to dermatologists are for one ofthree diagnoses: acne, warts and skin tumours. Thingsare very different in developing countries where overcrowdingand poor sanitation play a major part. There,skin disorders are even more common, particularlyin the young, but are dominated by infections andinfestationsathe so-called ‘dermatoses of poverty'aamplified by the presence of HIV infection.A sense of perspective is important, and this chapterpresents an overview of the causes, prevalence andimpact of skin disease.

Causes

The skin is the boundary between ourselves and theworld around us. It is an important sense organ, andcontrols heat and water loss. It reflects internal changes1 Skin disease in perspective. The most common categoriesof skin disorder in the UK

.Skin cancer, Acne, Atopic eczema, Psoriasis, Viral warts, Other infective skin disorders Benign tumours and vascular lesions, Leg ulcers, Contact dermatitis and other eczemas

Prevalence

No one who has worked in any branch of medicinewill doubt the importance of diseases of the skin.A neurologist, for example, will know all about theSturge–Weber syndrome, a gastroenterologist aboutthe Peutz–Jeghers syndrome, and a cardiologist aboutthe LEOPARD syndrome; but even in their ownwards they will see far more of other common skinconditions such as drug eruptions, asteatotic eczemaand scabies. They should know about these too.In primary care, skin problems are even moreimportant, and the prevalence of some common skinconditions, such as skin cancer and atopic eczema, isundoubtedly rising. Currently, skin disorders accountfor about 15% of all consultations in general practicein the UK, but this is only the tip of an iceberg of skindisease, the sunken part of which consists of problemsthat never get to doctors, being dealt with or ignoredin the community.How large is this problem? No one quite knows, asthose who are not keen to see their doctors seldomstar in the medical literature.

In the course of a single year most of those with psoriasis see nodoctor, and only a few will see a dermatologist. Somemay have fallen victim to fraudulent practices, such as‘herbal' preparations laced with steroids, and baselessadvice on ‘allergies'.Several large studies have confirmed that this is thecase with other skin diseases too.

• Of a large representative sample of the US population,31.2% were found to have significant skin diseasethat deserved medical attention. Scaled up, thesefigures suggest that some 80 million of the US population may have significant skin diseases.

• A community study of adults in the UK found 22.5%to have a skin disease needing medical attention: onlyone in five of these had seen a doctor within the preceding6 months. Self-medication was far more commonthan any treatment prescribed by doctors.• In another UK study, 14% of adults and 19% ofchildren had used a skin medication during the previous2 weeks; only one-tenth of these were prescribed by doctors. In a study of several tons of unused medicinalpreparations, 7% by weight were manufactured fortopical use on the skin

.• Preparations used to treat skin disease can be foundin about half of all homes in the UK; the ratio of nonprescribedto prescribed remedies is about 6 : 1. Skintreatments come second only to painkillers in the listof non-prescription medicines. Even so, in the list ofthe most commonly prescribed groups of drugs in theUK, those for topical use in skin conditions still comesecondabehind diuretics.Every 10 years or so we are given a snapshot of theway skin disorders are being dealt with in the UK, ina series of reports entitled Morbidity Statistics fromGeneral Practice.

Disability

Skin conditions are capable of ruining the quality ofanyone's life. Each carries its own set of problems. Atthe most obvious level, dermatitis of the hands canquickly destroy a manual worker's earning capacity,as many hairdressers, nurses, cooks and mechanicsknow to their cost. In the USA, skin diseases accountfor almost half of all cases of occupational illness andcause more than 50 million days to be lost from workeach year.

LEARNING POINTS  ‘Prevalence' and ‘incidence rates' are not thesame thing. Learn the difference and join asmall select band.(a) The prevalence of a disease is the proportionof a defined population affected by it at aparticular point in time.(b) The incidence rate is the proportion of adefined population developing the diseasewithin a specified period of time.2 A skin disease that seems trivial to a doctorcan still wreck a patient's life.

Depression

The physical, sensory and functional problems listedabove often lead to depression and anxiety, evenin the most stable people. Depression also seems tomodulate the perception of itching, which becomesmuch worse. Feelings of stigmatization and rejectionare common in patients with chronic skin diseases: upto 10% of patients with psoriasis that they think isbad have had suicidal thoughts.

Death

Deaths from skin disease are fortunately rare, butthey do occur (e.g. in pemphigus, toxic epidermalnecrolysis and cutaneous malignancies). In addition,the stresses generated by a chronic skin disorder suchas psoriasis predispose to heavy smoking and drinking,which carry their own risks.