Mark Twain wrote: "The finest clothing is a person's own skin..." Most of us aspire to have silky skin, soft to the touch. Why is that? Well, skin has been called a secondary sex characteristic, providing a pleasing sensation when in perfect condition; it also pleases us not to have rough skin, which can be uncomfortable. 

What keeps skin in this ideal state? The outermost part of the skin is called the stratum corneum or cornified layer. It is the first defense against the environment. It is kept smooth and efficient by being hydrated (water) and by fats (lipids). If, for whatever reason, it cannot do this for itself, we have to do it from the outside with moisturisers or emollients (from to mollify or soothe). Although water is necessary for skin hydration, drinking litres of the stuff will only flush out your kidneys but won’t plump up your skin! The water content of the skin is sealed in by an intact lipid layer, which may have to be provided by applying emollients. There are many medical names for dry skin – so, let’s try to demystify them here.

This is the medical name for dry skin. All of us will have had it from time to time, some of us will have been born with it, and others will develop it in certain circumstances. It is part of atopic dermatitis/eczema. Nearly everyone over 60 years has dry skin; post-menopausal females are unlikely to escape it. Those with chronic disease or malnutrition will have dry skin. Xerosis is brought on by cold weather, especially when we are swaddled in woolly jumpers. Low humidity and air conditioning are also hard on the skin, which they make dry to the touch and flaky. If ignored, on certain pressure areas like the fingers or heels, painful cracks (fissures) appear. They demand attention or else can become infected.

Hyperkeratosis is the name given to build up of scale or keratin so that it is packed into a thick layer. It may be referred to as a callus. It is found over pressure points, eg, the ball of the foot, on a toe (a corn) and finger tips in guitar players. Hyperkeratosis of the heels should never be ignored as fissures within can become infected. At whatever site it occurs, hyperkeratosis causes pressure on underlying tissue and so is often painful.

This is derived from the Greek word for fish, ichthys, not because the skin is wet and slippery, but because the scaliness often has the configuration of fish scales. It is not one disease, but covers a group of 65 types. We shall confine ourselves to the common type, ichthyosois vulgaris. Ichthyosis vulgaris affects one in 250 people; the characteristic skin appearances appear soon after birth. It is inherited and represents a genetic defect. Ichthyosis vulgaris may be associated with keratosis pilaris (that is, rough skin on the outer upper arms that has the feeling of a nutmeg grater) and hyperlinearity (pronounced skin lines) of palms and soles. Both these last two entities can also be found in people with atopic dermatitis.

You can choose to use either term - dermatitis or eczema - as they mean the same thing.

• Atopic dermatitis (AD) is an inherited form of dermatitis that is frequently associated with asthma and hay fever (rhinitis), and affects up to 20% of children. It usually presents in childhood and improves with age, but there is a severe adult form. The difference between it and dry skin is inflammation, which leads to itching, scratching and skin infection. The doctor will prescribe topical steroids and anti-itch medicine, but the mainstay of treatment is moisturising in order to soothe to help repair the damaged stratum corneum.
• Contact dermatitis (CD) occurs when something insults or damages the skin from contact with it. This can happen in two ways: the first is called irritant CD and is common. It can occur as in these Covid-19 times with frequent hand washing, the application of hand sanitiser and failing to moisturise immediately afterwards. The skin is red, sore and scaly and may fissure. Strong industrial oils handled without skin protection can do this, too. It is not an allergic reaction. Allergic CD occurs when the skin builds up a sensitivity to a certain chemical through repeated exposure. A common example is nickel sensitivity from jewellery, jeans studs and earrings. Another is allergic dermatitis from hair dye (paraphenylenediamine; PPD). There is no cure, only avoidance of the offending chemical, but topical treatment is necessary to restore the skin to normality. As in AD, the treatment of contact dermatitis (apart from avoidance of the cause) is the application of topical steroid preparations and emollients.

Psoriasis is a common inflammatory skin ailment that is inherited and affects up to 2% of the population. It occurs for the first time at any age, but usually in young adult life. It consists of red, scaly patches (plaques) on bony points like elbows and knees, but may be widespread. The scalp and nails are frequently involved. There is an associated arthritis in up to 15% of cases. It is not itchy like eczema. Psoriasis can be made worse by infections, stress and certain drugs; it is often better in summer as sunshine is beneficial for most patients. There are many treatments for psoriasis, but emollients have a part to play by reducing scale and soothing the inflamed patches.