Solar keratosis

 

What is solar keratosis?

Solar keratosis (also sometimes known as Actinic Keratosis) is a skin condition characterised by areas of thickened, scaly, raised areas of skin usually found on exposed areas of the body such as the face, upper back and the scalp of balding people. It is caused by the long term effects of exposure to the sun.

How is solar keratosis diagnosed

In most cases the diagnosis can be made quite confidently by the doctor simply on the appearance of the skin and the parts of the body involved. Solar keratosis is characterised by areas of skin which are rough and scaly in patches which generally range from very small areas to lesions several millimetres in diameter. They are sometimes flesh coloured but may be brownish and they feel rough and dry to the touch with occasional reddening of the surrounding skin.

As mentioned above, solar keratosis tends to occur on areas of the body which are exposed to the sun ie the face, the scalp of people with little or no hair and the upper shoulders and back and the backs of the hands. These areas tend not to be itchy or irritating but can result in small scales of skin falling off only to be replaced by more scaly skin. The patches do not generally get larger rapidly although over the course of many months or several years the patches may get bigger or be joined by other similar areas.

Sometimes an area of solar keratosis forms into a small horn-like growth called a 'cutaneous horn'which, although not dangerous, can be unsightly or may be prone to catch on clothing or other objects.

If there is doubt about the diagnosis of solar keratosis a biopsy (a small piece of skin from the affected area) may be taken and examined under the microscope.

 

What causes solar keratosis?

Solar keratosis is caused by the effects of long term exposure to ultraviolet light ie sunlight. Generally speaking skin can repair itself fairly well from minor damage caused by the sun but over a number of years of sun damage the skin becomes less able to deal with the harm caused by repeated exposure to ultraviolet light. Therefore it is not so much the recent episode of sunburn that is likely to result in solar keratosis but years of poor protection (in the form of sun lotion, clothing and hats) from the sun' rays which finally leads to the development of solar keratosis.

Who gets solar keratosis?

Leading on from the information above it can be seen that those most likely to develop solar keratosis are people who have had years of sun exposure, especially if they have not taken proper precautions against the sun's rays such as high factor sun cream, wearing a hat and staying indoors as far as possible when the sun is at its hottest in the middle of the day. Therefore sufferers tend to be in the older age group with it affecting between 5 and 15% of the population over the age of 40 with an increase in numbers with each decade of age after this.

Fair skinned people are particularly vulnerable to the effect of the sun as are men (and the occasional woman) with little or no hair on their scalp since the sun's rays impact directly onto the top of the head leading to a high concentration of ultraviolet exposure to this part of the body.

Some groups of people are frequently found to be sufferers of solar keratosis. These include those whose jobs entail working outdoors and older men who fought in the army in the desert before more was known about the long term dangers of ultraviolet exposure.

Another group of people who may be at particular risk of solar keratosis are those on immunosupressant drugs. These drugs are given to people as part of their treatment for conditions such as certain types of arthritis, some cancers and as anti-rejection treatment for transplant patients. Because immunosuppressant drugs reduce the body's ability to fight infection or repair itself, the ability of the body to recover from the damage caused by the ultraviolet rays is impaired thereby making them more liable to solar keratosis and skin cancer.

 

Is solar keratosis dangerous?

Solar keratosis itself is not dangerous. It causes little in the way of symptoms other than rough skin and some irritation. However, its significance is that it is potentially pre-cancerous ie a certain percentage of cases of solar keratosis develop into a type of skin cancer called Squamous Cell Carcinoma (SCC).

There is a lot of disagreement surrounding the question as to how likely solar keratosis is to convert into SCC. On the one hand it is thought that around 60% of cases of squamous cell carcinoma arise originally from solar keratosis. However, on the other hand there seems to be some agreement that the conversion rate of solar keratosis to SCC is between 0.1% and 10%. In other words it is thought that there is between a 1 in 10 and 1 in 1000 chance of an area of solar keratosis developing into a SCC.

However, it should also be pointed out at this stage that a large number of deposits of solar keratosis regress (get better) spontaneously without treatment

 

How is solar keratosis treated?

As mentioned above, a large number (somewhere between 20% and 70%) of patches of solar keratosis disappear without treatment although it is also thought that in about 15% of cases the condition is likely to recur in the same area.

If a patch of solar keratosis persists, a number of types of treatment exist:

  • So-called physical treatment: This may be in the form of excision (cutting the deposits of solar keratosis out), curettage (removing it with a special hot-wire cutting instrument called a curette) or cryotherapy (deep freezing the area of solar keratosis with the use of liquid nitrogen causing it to drop off a few days later). All of these are generally done under local anaesthetic.
  • Secondly, solar keratosis can be treated with topical (applied to the skin) medication. The most commonly used of these is a cream called 5-fluouracil (Efudix) which is generally only prescribed by a consultant skin specialist. 5-fluouracil acts by killing the abnormal cells and allowing new normal cells to grow back in their place. Other creams include Diclofenac gel (Solaraze), Imiquimod 5% cream and occasionally a cream called Tretinoin (Retin A).
  • A treatment called Photodynamic therapy is sometimes used to treat solar keratosis. This involves the application of a special cream called 5-aminolaevulinic acid (ALA) onto the area of solar keratosis for long enough for the substance to be absorbed into the affected skin cells (usually 3-6 hours). This makes the cells particularly sensitive to a light which is then shone onto the area for up to 45 minutes. The area then usually scabs over, falling off approximately three weeks after the treatment. Sometimes photodynamic therapy is repeated after a few weeks if deposits of solar keratosis remain.
  • In patients with extensive (widespread) solar keratosis or where the condition is resistant to other treatments systemic treatment (medication taken orally) exists in the form of something called Acitretin. This is something called a Retinoid and is only prescribed by a specialist since is it is a powerful drug. It is also sometimes used to prevent new areas of solar keratosis from forming in people at particularly high risk such as those on immunosuppressant treatment (see above).

If someone is taking Acitretin in tablet form is it important that they have regular blood tests to make sure the medication is not affecting their liver and it is also crucial that they do not become pregnant whilst on the drug since it can cause severe abnormalities to occur in the unborn child.

 

Can solar keratosis be prevented?

The more unprotected exposure someone has to the sun in their lives, the more likely they are to develop solar keratosis and/or certain types of skin cancer. Therefore, to reduce this risk it is best to:

  • Stay out of strong sunlight especially when the sun is at its height in the sky around the middle of the day (between 11am and 3pm). One way of judging this is that it is best to avoid the sun when the sun' height means that your shadow is shorter than you are.
  • When outside in sunny weather it is best to stay in the shade as much as possible, wear a hat, long-sleeved shirt and a high factor sunscreen of at least SPF (sun protection factor) 15 or above.