The skin, hair and nails

Skin

The skin is the largest of the human organs, with a complex anatomy ( Fig. 14.1 ) and a number of essential functions ( Box 14.1 ). It has three layers, the most superficial of which is the epidermis, a stratified squamous epithelium containing melanocytes (pigment-producing cells) within its basal layer and Langerhans cells (antigen-presenting immune cells) throughout. The packaging and distribution of melanin within the epidermal cells determines the depth of skin pigmentation.

The dermis is the middle and most anatomically complex layer, containing vascular channels, sensory nerve endings, numerous cell types (including fibroblasts, macrophages, adipocytes and smooth muscle), hair follicles and glandular structures (eccrine, sebaceous and apocrine), all enmeshed in collagen and elastic tissue, within a matrix comprising glycosaminoglycan, proteoglycan and glycoprotein.

The deep subcutis contains adipose and connective tissue.

Dermatoses (diseases of the skin) may affect all three layers and, to a greater or lesser extent, the various functions of the skin.

Hair

Hair plays a role in the protective, thermoregulatory and sensory functions of skin, and also in psychosexual and social interactions. There are two main types of hair in adults:

• Vellus hair, which is short and fine and covers most of the body surface.

• Terminal hair, which is longer and thicker and is found on the trunk and limbs, as well as the scalp, eyebrows, eyelashes, and pubic, axillary and beard areas.

Abnormalities in hair distribution can occur when there is transitioning between vellus and terminal hair types (e.g., hirsutism in women) or vice versa (androgenic alopecia). Hairs undergo regular asynchronous cycles of growth and, thus, in health, mass shedding of hair is unusual. Hair loss can occur as a result of disorders of hair cycling, conditions resulting in damage to hair follicles (such as scarring inflammatory processes), or structural (fragile) hair disorders.

Nails

The nail is a plate of densely packed, hardened, keratinised cells produced by the nail matrix. It serves to protect the fingertip and aids grasp and fingertip sensitivity. The white lunula at the base of the nail is the visible distal aspect of the nail matrix ( Fig. 14.2 ). Fingernail regrowth takes approximately 6 months, and toenail regrowth 12–18 months.

Common presenting symptoms

These include:

• A rash: scaly, blistering or itchy

• A lump or lesion

• Pruritus (itch)

• Hair loss or excess hair (hirsutism, hypertrichosis)

• Nail changes

Ask:

• When did the lesion appear, or the rash begin?

• Where is the rash/lesion?

• Has the rash spread, or the lesion changed, since its onset?

• Is the lesion tender or painful? Is the rash itchy? Is the itch intense enough to cause bleeding by scratching or to disturb sleep, as in atopic eczema and lichen simplex? Are there blisters?

• Do the symptoms vary with time? For example, the pruritus of scabies is usually worse at night, and acne and atopic eczema may show a premenstrual exacerbation.

• Were there any preceding symptoms, such as a sore throat in psoriasis, a severe illness in telogen effluvium, or a new oral medication in drug eruptions?

• Are there any aggravating or relieving factors? For example, exercise or exposure to heat may precipitate cholinergic urticaria.

• What, if any, has been the effect of topical or oral medications? Self-medication with oral antihistamines may ameliorate urticaria, and topical glucocorticoids may help inflammatory reactions.

• Are there any associated constitutional symptoms, such as joint pain (psoriasis), muscle pain and weakness (dermatomyositis), fever, fatigue or weight loss?

• Very importantly, what is the impact of the rash on the individual’s quality of life?

Past medical and drug history

Ask about general health and previous medical or skin conditions; a history of asthma, hay fever or childhood eczema suggests atopy. Coeliac disease is associated with dermatitis herpetiformis.

Take a full drug history, including any recent oral or topical prescribed or over-the-counter medications. Enquire about allergies not just to medicines but also to animals or foods.

Family and social history

Enquire about occupation and hobbies, as exposure to chemicals may cause contact dermatitis. If a rash consistently improves when a patient is away from work, the possibility of industrial dermatitis should be considered. Ask about alcohol consumption and confirm smoking status.

Document foreign travel and sun exposure if actinic damage, tropical infections or photosensitive eruptions are being considered. The risk of squamous cell and basal cell cancers increases with total lifetime sun exposure, and intense sun exposures leading to blistering burns are a risk factor for melanoma. The susceptibility of an individual to sun-induced damage can be determined by defining their skin type using the Fitzpatrick scale ( Box 14.2 ).

Ask about a family history of atopy and skin conditions.

The history of a skin disorder alone rarely enables a definite diagnosis, with perhaps the occasional exception: an itchy eruption that resembles a nettle rash, the individual components of which last less than 24 hours, is very likely to be urticaria; and an intensely itchy eruption that affects all body areas except the head (in adults) and is worse in bed at night should be considered to be scabies until proved otherwise.