Photoageing and cancer

PHOTOAGEING

What is it?

There appear to be two major ways in which skin may age. The first is genetically programmed, so-called intrinsic or normal ageing, affecting the skin all over your body. The second is photoageing and results from the long-term adverse effects of sun exposure. The degree to which skin photoages is also determined genetically to some extent, in that fair-skinned people who burn easily tend to photoage most rapidly. However, this also depends very much on how much your skin is exposed to sunlight over the years, whether through normal outdoor activities or sunbathing, or both.
It is possible to judge the degree of photoageing of your skin by comparing the appearance of your hips or buttocks with that of your face. Those areas normally covered by clothing are smooth and freckle-and wrinkle-free. Exposed facial skin, in contrast, may be liberally freckled in fair-skinned people, if they have had lots of sun exposure. In older people, it may be dry, thickened, yellowish, blotchy brown, deeply wrinkled and affected by thread veins. This difference between skin that is usually covered and that normally exposed is the result of photo-ageing of the sun-affected sites.

What causes photoageing?

Photoageing is the result of accumulated skin damage caused by UV radiation over the years. Just as for sunburn, it is the UVB wavelengths that have the greatest effect; however, UVA exposure also causes significant changes, although with a tendency to be deeper. These may affect you, particularly if you spend lots of time on a sunbed or sunbathing with a sunscreen that blocks mostly UVB.
When radiation-induced DNA damage in the epidermis and dermis is not fully repaired, the structure of these layers gradually deteriorates. In addition, the chemicals involved in the sunburn process apparently also harm the dermis, especially the supporting collagen and elastin fibres that help keep it wrinkle-free, although this damage may recover somewhat over time; the fibres can also be directly damaged by UV exposure. All this means that your skin becomes drier, rougher and often thicker, whereas thread veins and wrinkles slowly develop. In some people, however, the epidermis becomes thinner and more fragile.
In addition, the tanning cells gradually stop functioning in a consistent fashion, and your skin may well develop a brown blotchi­ness. It may often gradually become yellowish as well. All these changes together are the visible signs of skin photoageing.
Other factors besides sunlight exposure may contribute to skin ageing, particularly cigarette smoking, and make the overall skin appearance even worse.

Can photoageing be prevented?

In theory, yes. If you could protect your face from the sun all the time, it should remain relatively young-looking and wrinkle-free into old age. In the past, however, this has rarely happened, particularly because people have not been aware of the cause of photoageing.
First, it is vital to begin any protection programme very early in life: it has broadly been estimated that up to 50 per cent of our total UV radiation exposure is acquired by the age of about 18 and 75 per cent by 30; thus we can improve the outlook for our children’s skin by acting now. As far as adults are concerned, however, the ‘time­clock’ for photoageing has already been ticking for some time, but we can definitely minimise further changes by being careful in the sun from now on.
Second, it seems likely that skin photoageing may develop even with recurrent minor UV exposure. Increasing evidence suggests that even walking to and from the office or shops or hanging out the washing may expose our skin to enough sunlight to cause some photoageing. The skin does not apparently need to burn, or even turn pink, for that damage to take place. This therefore means that preventing photoageing probably requires even more long-term effort at sun protection than sunburn does.
In summary, any steps that you take now to cut down your time outside unprotected will reduce the speed and extent of your eventual skin photoageing, whenever you may start. Although your face may not look as young as your buttocks, it can still look much better than if you did nothing at all to protect it. The younger you are when you start your protection programme, the better your outlook. To do this, you should reduce your exposure even to ordinary daylight each day, rather than just avoiding sunburn. To assist you in this, some types of make-up and moisturisers now incorporate sunscreen ingredients and can be very worthwhile if you are happy to use such products. For more on the prevention and treatment of sun damage and photoageing.

WHAT IS SKIN CANCER?

All cancers appear to be made up of body cells that have gradually deteriorated through sequential damage to their DNA, making them start to grow independently of the rest of the body and infiltrate other tissues. To do this, they must bypass the usual mechanisms designed to prevent this happening. They are dangerous because not only can they affect and damage the normal structures around them, but also they can sometimes later spread through the bloodstream and lymph vessels to disrupt other parts of the body, growing and causing disruption at these new sites, which are often vital organs such as the lungs, liver and brain. In the end stages, they may also divert nourishment from the body’s normal activities to meet their own requirements.
DNA-damaging agents are known as carcinogens, and include, for instance, chemicals in tobacco smoke, certain food constituents, radioactive emissions, certain viruses and, as far as skin is concerned, the UVB and UVA in solar radiation.
There are three main types of skin cancer (or carcinoma) (see box below). In addition, there are two cancer precursor lesions: the solar (or actinic) keratosis, which may sometimes develop into squamous cell cancers, and lentigo maligna, which may precede one form of melanoma, the lentigo maligna type. Basal cell cancers and other melanomas do not have precursors.
Skin cancer is one of the most common cancers worldwide. In the UK alone there are approximately 50,000 new cases each year; of these, about 30,000 are basal cell cancers, nearly 10,000 squamous cell lesions and 5,000 malignant melanomas. About 2,000 people die each year from these disorders, most of them from melanoma. Nevertheless, most skin cancers are avoidable and all are generally curable if caught early, which is why dermatologists and health campaigners are widely publicising all forms of the condition and how to prevent them.
Despite these efforts, there have been continuing substantial increases in all types of these tumours over the last few decades, with rates tending to double every 10 to 12 years. This to some extent is the result of improved diagnostic techniques and greater longevity, but is probably mostly to do with lifestyle changes in recent years. We now take far more sunshine holidays than we once did, and many people spend much of their leisure time in this country sunbathing. Any effects from ozone depletion have yet to be felt, but if such depletion continues unchecked, skin cancer risk could increase further. On the other hand, the possible good news is that annual skin cancer rates now appear to be increasing a little more slowly, perhaps as a result of major efforts at public education.

Basal cell cancers

Basal cell carcinoma is the most common and least aggressive form of skin cancer, developing from the basal layer of the epidermis. This tumour normally grows slowly, often appearing first as a small, flesh-coloured, firm, slightly pearly nodule, often on the upper face, shoulder or back of an older person. It then slowly enlarges until a central area of broken skin develops, which is when some people first notice the problem. Sunlight plays a major part in causing this cancer, but other factors are also important, because not all exposed areas are regularly affected, particularly the backs of the hands, for example.
In addition, although older people most commonly develop the disorder, it can also occur in younger people. The main danger from basal cell cancer is its potential to erode the skin and underlying tissues relentlessly over many years, although fortunately it never spreads to the rest of the body. Treatment is straightforward if early.

Solar (or actinic) keratoses

Solar keratoses result from the early disordered growth of groups of epidermal keratinocytes, generally on skin that has been continually exposed to the sun, such as on the face, ears, backs of hands and scalps of men with thinning hair.
Such lesions are very common, affecting a third or more of fair-skinned people over the age of 60, particularly in sunnier climates. They are usually less than a centimetre across, reddish or brownish, scaly or rough, slightly uncomfortable if knocked and sometimes easier to feel than to see. You can check for them by running your fingers or palm of your hand lightly over your exposed skin – they are usually slightly rough and sore patches compared with normal. There are of course other causes for rough skin, but any persistent patches just might be solar keratoses.
Solar keratoses are possible precursors of squamous cell carci­noma, but rarely progress in practice; only a few ever become malignant and some may actually disappear, particularly if sun exposure is minimised. Failing that, their treatment is relatively straight­forward, by freezing or cutting them out, treating them with creams or using so-called photodynamic therapy as detailed on page 56. It is generally worthwhile to have such treatment to avoid the slight risk of future squamous cell cancer, as well as to get rid of the often unsightly, slightly sore patches.

Squamous cell cancers

Squamous cell carcinoma is the second most common type of skin cancer; it also develops within the keratinocytes of the epidermis. This disorder is rare in people under 50, most commonly affecting relatively fair-skinned individuals who have been exposed to regular sunlight over long periods of their lives in sunny climates, or with their work or hobby. Typical lesions are slightly tender, reddish or brownish, slowly growing, persistent lumps on any regularly exposed skin; generally they are more bulky and rougher to the touch than basal cell cancers. They generally start as small patches, sometimes as solar keratoses, and you should always consult your doctor about any lump or sore of this type which fails to heal over weeks to months. The treatment of squamous cell cancers is usually straightforward, generally excision and, except in the latest stages, normally leads to a complete cure.

Malignant melanoma

Malignant melanoma is the rarest skin cancer, making up only about 10 per cent of such cancers, but it is also the most dangerous, causing more than 75 per cent of all deaths from the disease. If caught early, however, as with all other skin cancers, it is readily curable, so it is extremely important to look out for and recognise the early signs of this aggressive condition. It consists of a collection of cancerous melano­cytes, the tan-producing cells of the basal epidermis, and usually appears as a mole larger than about five to six millimetres across (the size of the blunt end of a pencil), which irregularly enlarges and darkens over several months; consult your doctor promptly if you have any mole that behaves like this. Many melanomas seem to develop within pre-existing moles, although others apparently develop from normal skin. The condition is most common in but by no means restricted to those who are very fair, tend to freckle easily, already have lots of moles and have been sunburned frequently. Younger age groups are regularly affected, mostly on the trunk (in men) and lower leg (in women), whereas elderly people may develop them on the face, in a relatively less aggressive form. This last type often follows months to years of the presence of an initially harmless, fixed, irregular, brown discoloration called a lentigo, later a lentigo maligna.
Malignant melanoma can in fact develop at any age, not infrequently in youngish adults, although it is more common in those over 50, and very uncommon before the age of 16. In addition, it is still rare overall, affecting only about one in 10,000 people per year in the UK or around 5,000 in total, although rather more of course among those at greater risk.
The so-called ABCDE guide summarises the signs to look out for; these changes often, though not always, occur together, and then progress over the following weeks to months.

Many people may develop new, harmless, evenly coloured, regularly outlined moles from time to time, particularly around the teenage years, but sometimes much later in life as well. These are generally nothing to worry about, but if you have any doubts at all it is best to consult your doctor, particularly as the treatment for melanoma is straightforward in the early stages and essentially always fully curative; the procedure for this is explained later.

WHAT CAUSES SKIN CANCER?

There is now little doubt that the most important cause of skin cancer is excessive exposure of the skin, particularly if pale, to the UV radiation in sunlight.
As for sunburn and photo-ageing, it seems certain that the UVB component of this radiation is the most important culprit. As stated earlier, these rays are well known to damage skin cell DNA, which governs the structure, growth, function and reproduction of cells. If such damage is not repaired accurately, it may eventu­ally contribute to the development of cancer, probably through a sequence of changes occurring over a number of years. In addition, the UVB exposure responsible almost certainly reduces the ability of the skin’s immune system to eliminate any early cancers at the same time.
As skin cancer is thought to be a step-wise process, probably requiring at least several separate DNA changes during development, there is often a very long time lag between the initial damage, such as during sunburn in childhood, and the eventual occurrence of the cancer. During this period additive sun damage must also take place. This total time lag may be 30 to 50 years, particularly for squamous cell cancers, or often less at 10 to 15 years for basal cell cancers and melanomas. The length of this delay clearly depends heavily on the degree of continuing sun exposure and on the individual’s skin type.
Nevertheless, some people with skin cancer feel that they can never sunbathe or even go out in the sun at all. This would generally occur only in very fair-skinned individuals because they are very sun sensitive, and repeated minor exposures in their early lives and young adulthood may have been major factors in their cancer development. On the other hand, some people who work or spend a great deal of leisure time outside simply pay no attention to whether they are in the sun or not. Thus, someone who has skin cancer today, for example, may have seen a lot of sun while on National Service when young in the Far East, or during a childhood spent on a farm, or perhaps through sunbathing every summer as a teenager or young adult, and people with such histories should therefore take continuing care. Cutting down on sun exposure at any age is likely to reduce signifi­cantly the future development of solar keratoses or skin cancers.
The relationship between sun­light exposure and skin cancer is most clear-cut for solar keratoses and squamous cell cancers, almost all of which develop on skin that is constantly exposed, such as on the face and backs of the hands. For malignant melanoma, however, such a relationship, although still based on strong evidence, is less easy to understand. This type of cancer is more common in fair-skinned people who have lots of moles, particularly unusual ones, and in those who have excessively but intermittently sunbathed and burned a lot. A melanoma, if it occurs, generally appears on one of the areas that was intermittently exposed and burned, such as the trunk or lower leg. This strongly suggests that repeated bursts of intense sun exposure causing sunburn on usually covered skin are most likely to induce melanomas and this behaviour should be avoided.
In addition, we don’t fully under­stand the exact association between sun exposure and basal cell cancers, and other factors besides sunlight again appear to be involved such that lesions occur more commonly on some exposed parts of the skin than others and even rarely without sun exposure; however, the relationship with sunlight is thought overall to be similar to that for melanoma.

The very strong association between sun exposure and skin cancer development suggests that up to 90 per cent of such cancers could be prevented if people took proper steps to protect their skins from sunlight from an early age.

WHO IS AT RISK?

People with skin types I, II and III, namely all those with fair skins, are most most likely to develop skin photoageing and cancer: the fairer the skin, the greater the risk. Further, people who sunbathe, work outdoors for large parts of their lives, enjoy outdoor hobbies, such as cycling, gardening, tennis, cricket or golf, or live in sunny climates at low latitudes, are particularly likely to be affected.
As stated earlier, some people with skin cancer may claim never to have sunbathed or worked outside, and therefore wonder how they developed the condition. In most cases, the answer is that they are very fair-skinned and have been exposed a lot as a child or repeatedly for short periods over many years, usually during routine activities such as walking to and from the office, sitting outside in summer for a sandwich at lunchtime or gardening. Although not proved conclusively, cigarette smoking may perhaps increase any skin cancer risk.
People at risk of melanoma usually also have a fair skin, although other factors are likely to be important as well, as far as they are concerned. Those with large numbers of moles, particularly oddly shaped ones, and those with a family history of melanoma, are especially liable to develop the condition, particularly if they have sunbathed and burned a lot. Similarly, basal cell cancers appear to be associated with other, as yet uncertain, causative factors besides sunlight, and occasionally with a family history of the condition, although fair skin and frequent excessive sun exposure are again likely to be very important.

CAN SKIN CANCER BE PREVENTED?

Skin cancers can largely be prevented. It is estimated that over 90 per cent of such lesions are avoidable by reducing your exposure to UV radiation. You can best achieve this by doing the following with this order of priority:

• Try to undertake outdoor activities, in summer, tropical climates or at altitude, outside the hours of 11:00 to 15:00, namely when the sun is lower in the sky, even on cloudy or cool days. This is even more important if there is a lot of sky visible, or if there are white surfaces, snow or areas of rippling water nearby. If you must sunbathe, do it outside these situations, as the UV intensity is much weaker then, even if the weather is hot and sunny.

• Wear suitably protective clothing where possible, such as a broad-brimmed hat, a longish-sleeved, loosely fitting, close-weave top, and a similar form of apparel for the legs; in the UK and some other countries, special UV-protective clothing is available, and this may be used instead for greater reliability.

• Routinely use liberal amounts of a sunscreen that is highly protective against both UVB and UVA on exposed skin when you are outside, particularly between the hours of 11:00 and 15:00 in summer, in the tropics and at altitude. Re-apply such preparations every hour or so, particularly after swimming or exercise.

• All this advice is even more important for young children, who have more sensitive skins, are unaware of the implications of excessive sunlight exposure and also have lots of free time to spend outside.