The skin is often referred to as the largest body organ and serves as the main protective barrier against damage to internal tissues from trauma, ultraviolet light, temperature, toxins and bacteria. The skin is also responsible for sensory perception, temperature regulation, production of vitamin D and excretion of waste products. In addition to preventing harmful substances from entering the body, it also controls the loss of vital substances from the body. It is therefore important that the skin remains intact to allow the body to perform these essential functions.
The skin contains a number of accessory organs which assist in its protective role. It consists of two main layers: the epidermis, or outer layer, and the dermis, which lies beneath the epidermis.The thickness of the skin varies depending on the site, with thicker skin being present on areas of the body that experience friction or wear and tear, such as the soles of the feet and palms of the hand. The skin is supported by a layer of fatty tissue, sometimes known as the hypodermis. This fatty area helps to act as a cushion to protect the body and is also important for insulation.
Common skin conditions in adults
Acne is a disorder of the pilosebaceous unit which may present with comedones, inflammatory papules or pustules. Nodules and scarring can also occur. The precursor lesion of all acne lesions is the microcomedone which, under the influence of androgens, develops into non-inflammatory lesions (comedones) and inflammatory lesions (papules and pustules). Lesions of acne vary considerably with time, but in acne vulgaris comedones are always present and are a diagnostic sign. Most patients notice a fluctuation in the number and severity of spots. In young women, this is often related to the menstrual cycle.
Acne occurs on the face, chest and back depending on the distribution of sebaceous follicles in the individual.
Type of lesion Non-inflammatory lesions:
• open comedones (blackheads)
• closed comedones (whiteheads).
• Papules and pustules – the majority of patients with comedonal acne develop papules and pustules. They are the well known little red spots or pustules on a red base. They may be itchy or quite painful. Papules develop rapidly over a few hours and frequently become pustular as they evolve. They generally resolve over a few days.
• Nodules and cysts – as the inflammation within the pilosebaceous unit progresses and extends deeper into the dermis, the size of visible and palpable lesions increases, resulting in deep-seated nodules.
• Scars – the inflammatory process of acne can cause scarring. Characteristically, small, deep “ice-pick” scars occur, but more severe disease will leave gross changes with atrophy or keloid formation.
• Individual lesions usually last less than two weeks but deeper papules may persist for months. The average “acne life” is 12 years.
This is an infection of the subcutaneous tissues most commonly caused by a group A, C or ß-haemolitic streptococcus. It usually affects a lower limb but can occur anywhere on the body. More common in older people but can be seen in all age groups.
There is usually an obvious portal of entry for the organism such as a leg ulcer, tinea pedis between the toes (athlete’s foot), eczema on the feet or legs or an insect bite. The area will be erythematous and oedematous with localised pain and restricted mobility. Blisters may be present with areas of skin necrosis. The patient may also have systemic symptoms such as fever, malaise, chills or possibly rigors.
Psoriasis is a common disease which affects about 3% of the population. Psoriasis typically waxes and wanes with periods of relapse and remission. It is probably linked to several genes so occurrence within families varies. It may be precipitated by hormonal changes, infection such as a streptococcal throat infection or trauma. Medications and emotional stress can also be a trigger. There are several different forms of psoriasis. Here we describe two of the more common presentations: chronic plaque psoriasis and guttate or small plaque psoriasis
Chronic plaque psoriasis
The lesions are bright red with clearly defined edges and a silvery scale. The scale will flake off easily. The lesions tend to be symmetrical, commonly affecting the scalp, elbows, knees, sacral area and lower legs. The appearance will be quite different if flexural areas such as axillae, groins, sub-mammary or natal cleft are affected, presenting as smooth and non-keratotic with a shiny glazed appearance. This mainly affects older patients but can also present in children. Note that fungal or bacterial infection may also be present in flexural areas. The genitals, palms, soles and nails may also be affected in some individuals. Most patients have a few stable plaques but psoriasis can become unstable and extensive. A small proportion of patients will have joint involvement (psoriatic arthropathy).
Guttate/small plaque psoriasis
This is an acute form of psoriasis which appears suddenly, often after a streptococcal throat infection. The lesions are typical of psoriasis − bright red, well demarcated with silvery scale − but are uniformly small (0.5−1.0cm in diameter). The rash can be very widespread. It often resolves spontaneously in about 2−3 months. It may be the first episode of psoriasis for the patient but it can occur in someone who has had psoriasis for years
Shingles (herpes zoster)
Shingles occurs in people who have previously had chickenpox. The virus lies dormant in the dorsal root ganglion; when reactivated, it travels down the cutaneous nerves to infect the epidermal cells
There is pain, tenderness or an abnormal sensation in the skin for several days before the rash appears. The rash will form groups of small vesicles on an erythematous background, followed by weeping and crusting. The rash is usually unilateral with dermatomal distribution and a sharp cut off at or near the midline. This feature and associated pain makes any other diagnosis unlikely. The pain often continues until healing occurs but may go on for months or even years in older people (post-herpetic neuralgia).
Excessive exposure to ultraviolet radiation is linked to non-melanoma type skin cancers and malignant melanoma. Early recognition is most important. A good rule of thumb is to seek medical advice about all lesions which are not healing and may be enlarging. Here we describe the two most common forms of skin cancer and malignant melanoma. Biopsy is usually performed to assess the lesion histologically.
Basal cell carcinoma (BCC, rodent ulcer)
This is the commonest skin cancer. It usually occurs in fair-skinned people who have worked or had hobbies out of doors. Although due to sun damage, BCC does not occur at the sites of maximum sun exposure (it rarely appears on bald scalps, the lower lip or dorsum of the hand). Most occur on the face, with some on the trunk and limbs. Metastatic spread is rare in BCC
BCC commonly starts as a small translucent (pearly) papule with telangiectasia over the surface. It slowly increases in size and, over time, the centre may ulcerate and crust (rodent ulcer). On examination, if you stretch the skin you will see a raised rolled edge like a piece of string sitting around the edge.
Squamous cell carcinoma (SCC)
Although less common than BCC, SCC is an invasive carcinoma which is faster growing than a BCC and may metastisise if left untreated. It can arise from previously normal skin or from a pre-existing lesion (such as Bowen’s disease and actinic keratosis). SCC occur on sun-exposed skin which shows signs of sun damage. Common sites include bald scalp, lower lip, cheeks, nose, top of ear lobes and dorsum of the hand. They can also appear on non sun-exposed sites such as a site of previous radiotherapy or chronic scarring of burns and leg ulcers
A hard nodule of indurated skin which may have increased in size quite rapidly and may have ulcerated. Lesions bleed easily. Well-differentiated tumours produce keratin, so the surface will be scaly or even horny and are often painful to touch.
A malignant melanoma is a malignant tumour of the pigment-producing cells (melanocytes). Two thirds arise from normal skin and one third from a pre-existing mole. Numbers are increasing. It is the most dangerous of the skin cancers as it has the capability to metastisise through the lymphatic and circulatory systems
New moles developing or change in appearance; bleeding or crusting; increase in size; irregular outline; irregular pigmentation; pain or itch. Early diagnosis is important. If the lesion is superficial (that is, it has not invaded downwards into the dermis), excision is more likely to result in cure.
Vasculitis is an inflammation of the blood vessels in the skin, usually due to the deposit of immune complexes in the walls of the vessels.
The presentation will differ depending on the size and site of vessels involved. If the capillaries are involved, there will be a polymorphic rash with palpable purpura, as well as macules, papules, vesicles and pustules. If there is arterial involvement, livedo reticularis, nodules and ulceration of the lower leg may be present. Where there is arterial and venous involvement, there will be red, tender nodules or deep plaques in the subcutaneous fat.
Vasculitis has numerous causes, including:
• infection (e.g. streptococcal infection)
• collagen vascular disease (e.g. systemic lupus erythematosus (SLE), rheumatoid, systemic sclerosis)
• plasma protein abnormalities
• drugs (e.g. allopurinol, barbiturates, carbimazole, thiazide diruetics)
• idiopathic (no cause found)