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Principles of dermatological practice

An overview of dermatology

Created 2008.

Learning objectives

  • Develop an understanding of the scope of dermatology
  • Describe the training required to be a dermatologist
  • Describe the epidemiology of skin diseases and their psychosocial impact


Dermatology is the branch of medicine that deals with skin, mucous membranes, hair and nails. Although relatively straightforward to examine, the skin is the largest organ and has numerous potential abnormalities - there are about 1500 distinct skin diseases and many variants. We are relatively ignorant about the pathogenesis of the majority of these although knowledge is rapidly increasing especially in the fields of molecular medicine and genetics.

This course will discuss the impact of skin diseases, outline the biology of normal skin, and describe how to examine the skin and how its diseases may be effectively treated. A range of skin infections, inflammatory skin diseases and neoplastic conditions will be briefly described.

UK data suggests an average of 15% of consultations in general practice relate to a skin problem and between 50 and 75% of individuals may have a skin problem at any time. Although most of these are relatively harmless and asymptomatic, (warts, athletes' foot, dandruff, insect bites and so on), many result in significant disability.

Symptoms of skin disease include:

  • Pain, especially stinging and burning
  • Itch, which may be intermittent or persistent, localised or generalised
  • Functional disability

Signs may be described in terms of single areas of altered skin (lesions) or widespread eruptions. The distribution, configuration, colour, morphology, surface and secondary changes may be helpful in making a diagnosis and planning management.

Classification of skin diseases

Skin diseases are classified in various ways.

  • Site of involvement such as facial rashes, lesions on sun-exposed sites
  • Pathogenesis (when known) such as genetic abnormalities, infectious aetiology or autoimmune mechanisms
  • Main structure affected such as epidermal diseases, abnormalities of melanocytes, vascular changes.

However, these classifications are evolving as the science of dermatology expands. The importance of genetic predisposition and immune function are increasingly recognised.

Reed codes, DRGs and the International Classification of Diseases (ICD-10) are not adequate for dermatological diagnoses.

There have been various attempts to name and categorise skin diseases and these are evolving. Confusion in terminology has resulted in several names for the same disorder, and several different disorders have been given the same name. The British Association of Dermatologists (BAD) Index is a comprehensive list, with subclasses allowing up to six figures/letters for precision. There is overlap where a specific condition may be assigned more than one code.

Summarised BAD index codes (1999)

A. Infectious diseases affecting the skin
B. Reactions to mechanical, thermal, cold and radiation stimuli
C. Dermatitis/eczema and related conditions
D. Psoriasis and other acquired keratinising disorders
E. Papulosquamous and granulomatous disorders of the skin
F. Urticarias, erythemas and other inflammatory dermatoses
G. Disorders of skin colour
H. Disorders of skin appendages
J. Disorders involving cutaneous vasculature
K. Disorders of the dermis and subcutaneous tissue
L. Site-specific dermatoses
M. Connective tissue, immunobullous and related diseases
N. Metabolic and nutritional disorders affecting the skin
P. Psychological, psychiatric and neurological disorders affecting the skin
Q. Cutaneous markers of internal disorders
R. Dermatoses resulting from treatment or from poisons
S. Genetic and chromosomal disorders affecting the skin
T. Dermatoses specific to age or sex
W. Naevi, hamartomata and developmental anomalies of the skin
X. Neoplasias, tumours and cysts of the skin and appendages
Y. Benign and malignant infiltrations of the skin
Z. Diagnosis not coded

An online database of dermatological terminology, DermLex the Dermatology Lexicon, is now accessible on the American Academy of Dermatology's website (September 2009).

Epidemiology of skin diseases

Certain skin problems may be more prevalent in specific populations.

What conditions do you think white-skinned New Zealanders are particularly prone to?

White-skinned New Zealanders are particularly prone to conditions relating to excessive exposure to ultraviolet radiation in skin that has inadequate natural protection. These include photoageing changes (e.g.. dryness, freckling, fine wrinkles) and malignancies (e.g. actinic keratoses, basal and squamous cell carcinoma, melanoma).

Sun damaged skin

Black skin is particularly prone to pigmentary disorders and hypertrophic or keloidal scarring.

Trichrome vitiligo

Skin diseases prevalent in the tropics often have infectious origins.

  • Bacterial infections, usually impetigo but also tropical ulcers, yaws, cutaneous tuberculosis and pinta
  • Widespread fungal infections, usually dermatophytes but also mycetoma
  • Parasitic infections, usually scabies but also leishmaniasis and schistosomiasis
  • Viral haemorrhagic fevers
Tropical skin infections

Occupational dermatological diseases often relate to the irritant nature of material with which workers are in contact and sometimes to immune reactions to specific allergens. Hand dermatitis is the most common occupational skin problem. Examples:

  • Cleaners develop irritant hand dermatitis due to water, detergents and solvents; and may be allergic to fragrances, formaldehyde or preservatives.
  • Hairdressers develop irritant hand dermatitis due to water, shampoo and hair fibres; and may be allergic to nickel, hair dye, bleach or perming solution
  • Builders develop irritant hand dermatitis due to cleansing agents, friction, fibreglass and cement (strongly alkaline); and may be allergic to epoxy resin (especially boat builders), potassium dichromate (a component of cement) or formaldehyde (timber treatment).
  • Dairy farmers may develop chilblains (early morning milking), paronychia (cold wet fingers) or contact dermatitis due to allergy black rubber hosing.
Occupational hand dermatitis

Psychosocial impact of skin diseases

What are the the occupational and social impacts of the conditions illustrated below?


Disfiguring skin disorders

Most dermatological conditions are highly visible and may invoke disgust, shame and self-consciousness that can have profound psychosocial effects. Disfigurement can result in negative self perception, depression, social rejection and social isolation related to unfavourable self-image. Emotional abuse, verbal abuse and bullying may take place. These in turn can lead to self-contempt, frustration and torment leading to deliberate self harm or even suicide (a recognised complication of disfiguring skin conditions such as acne).

  • Skin conditions affecting the face may require aggressive treatment even if they are clinically relatively mild.
  • Disturbance of body image is particularly serious if it arises during childhood or adolescence, as is the case for birthmarks, atopic eczema and acne.
  • Patients with body dysmorphic disorder (dysmorphophobia) believe they are ugly, unattractive or even repulsive despite a normal appearance. Preoccupation with their appearance may be a sign of obsessional-compulsive disorder and may lead to severe depression.

In addition, psychiatric disorders may manifest as apparent skin disease. Therefore the management of skin diseases requires recognition of psychological aspects as well as treating the affected skin.

  • Psychoses may present as delusions of parasitosis, a false but unshakeable belief that they are infested and resulting in scratching and gouging the skin.
  • Other patients deliberately harm their skin and may present with strangely shaped burns, ulcers or rashes. This is called dermatitis artefacta.


Outline pharmacological, cognitive and behavioural management of body dysmorphic syndrome


Related information


On DermNet NZ:

Information for patients

Other websites:

Books about skin diseases:

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