Solar Keratosis

What is a solar keratosis?

A solar keratosis is a small, thickened, scaly growth which develops on the skin. It is the most common skin condition resulting from sun-damaged skin. It is caused by excessive exposure to ultraviolet (UV) rays from the sun over many years. Solar keratoses are also known as actinic keratoses.

What does a solar keratosis look like?

Each can range from the size of a pinhead to 2-3 cm across. Their colour can be light, dark, pink, red, the same colour as your skin, or a combination of these. The top of each one may have a yellow-white, scaly crust. Redness may develop in the surrounding skin. The picture shows a solar keratosis on an ear.

Solar keratoses feel rough and dry, and are slightly raised from the surface of the skin. Often it is easier to feel rather than see them. They can also be hard and warty. Sometimes hard skin grows out of a solar keratosis like a horn (called a cutaneous horn).

Several solar keratoses may develop at about the same time, often in the same area of skin. Sometimes they can join together and form a large, flat-ish, rough area of skin.

Solar keratoses usually develop on areas of skin which have received a lot of sun exposure. Skin on the face, neck, ears, bald patches on the scalp and the backs of the hands is commonly affected. They may also appear in other areas (such as the back, chest and legs) in people who do a lot of sunbathing. There are usually no other symptoms. Rarely, you may get an itchy or prickling sensation from affected areas of skin.

Who gets solar keratoses?

Solar keratoses are caused by damage to the skin by UV light which is part of sunlight. The skin is normally good at repairing any minor damage. But, over the years some areas of skin are unable to cope with the repeated exposure to sun and a solar keratosis can form. So, it is not a recent bout of sun-tanning that causes them but repeated minor sun damage to the skin over time.

People with fair skin who do not tan easily are most commonly affected, especially those with blue/green eyes and blonde/red hair. Because their skin has less protective pigment, these people are the most susceptible to sunburn and other forms of sun damage. Solar keratoses can occur in people with darker skin, but they are almost unheard of in black-skinned people.

As it usually takes years of sun exposure to develop a solar keratosis, older people tend to be most commonly affected. Solar keratoses are more common in those aged over 50 years. But, they may appear at a much earlier age in people who work outdoors (such as construction workers, farmers etc), or who do a lot of sunbathing or use sunbeds frequently. In the UK, about 1 in 3 men and 1 in 5 women over the age of 70 have (or have had) actinic keratoses. They are more common in men, mainly because men are more likely to have outdoor occupations.

Solar keratoses are more common in people who have a suppressed immune system, such as people who have had organ transplants (because they take long-term anti-rejection medication), people who have had chemotherapy to treat cancer and people with HIV infection. However, even in such people, they do not occur without exposure of the skin to the sun.

What happens to solar keratoses?

Three things can happen to a solar keratosis. This is important when considering treatment:

  1. The solar keratosis may regress. This means it clears away on its own, without treatment.
  2. A solar keratosis may persist. So, it remains, doesn’t change but doesn’t disappear either.
  3. It might progress into a skin cancer (see below).

Are solar keratoses dangerous?

In themselves, solar keratoses are not cancerous and do no harm. But, they can sometimes be unsightly. Up to about a quarter of solar keratoses will clear away by themselves without any treatment over the course of one year.

However, in people who have between seven and eight solar keratoses on their skin, there is about a 1 in 10 chance that one will turn into a form of skin cancer called squamous cell carcinoma (SCC) over a 10-year period. This is not the most serious form of skin cancer (melanoma). It is a fairly slow-growing cancer and can usually be easily cured if treated early enough. This means that solar keratosis can be seen as a potentially premalignant condition of the skin (a precursor to cancer).

(See separate leaflet called ‘Cancer of the Skin – an Overview’ and ‘Cancer of the Skin – Non-melanoma’ for more information.)

Some solar keratoses become cancerous because the UV exposure from the sun’s rays, causes changes (mutations) in the genes on the DNA of skin cells. This causes skin cells to divide and grow abnormally, instead of just repairing damage. The abnormal cells tend to multiply in an out of control way – this causes a tumour (lump).

How are solar keratoses diagnosed?

Your GP may be able to diagnose a solar keratosis by its typical appearance alone. Sometimes this is difficult and, if doubt exists, you may be referred to a dermatologist (skin doctor). A dermatologist will examine the skin more closely, perhaps with a dermatoscope. This is a magnifier with a light that helps to distinguish between benign (harmless) skin lesions and malignant (cancerous) ones. Sometimes is is necessary to take a biopsy of the skin lesion. This means that a small sample of skin is taken and examined under the microscope in a laboratory. A biopsy means that the cells in the skin can be seen and an accurate diagnosis can be confirmed.

What is the treatment for solar keratoses?

No treatment may be an option

Without treatment up to a quarter of solar keratoses will disappear within a year. If you only develop one, your doctor may advise that you leave it alone (provided it is not causing any symptoms). It may go away, but see a doctor if you notice any change in the appearance or if it becomes tender. You may be advised to apply an emollient (moisturising) cream to help soften the skin around the solar keratosis. You may also be advised to apply sun cream with a high sun protection factor (SPF). High factor sunscreens also moisturise, but importantly they will prevent further sun damage to the skin (and hopefully prevent the development of further solar keratoses).

If treatment is advised, there are several options. The method that your doctor advises depends on factors such as the number of solar keratoses that you have, where they are and how big or thick they are, your health and your preferences.

Freezing a solar keratosis with liquid nitrogen

This is a common treatment in people who have small numbers of solar keratoses. It is also called cryotherapy or cryosurgery. Liquid nitrogen is so cold that it destroys tissue. A solar keratosis can be easily sprayed with liquid nitrogen. It is destroyed and then falls off a few days later. A small scab is left and is gradually replaced by fresh healthy skin. Liquid nitrogen often causes the surrounding skin to blister for a few days. Sometimes this form of treatment can leave a white spot on the skin after treatment.

A cream or gel

Topical treatments (meaning you apply them to the skin) are useful if you have a lot of small solar keratoses where you would otherwise need repeated freezing to get rid of them all. Creams, gels (water based) and ointments (greasier) are available.

  • One type of gel contains an anti-inflammatory medicine called diclofenac (brand name Solaraze®). Usually at least three months of treatment is needed. Side-effects may include itching and a rash.
  • Another cream which is sometimes used contains a medicine called fluorouracil (brand name Efudix®). This kills the abnormal cells and fresh normal skin grows back. This cream is usually applied for 3-4 weeks but it can cause significant (but temporary) inflammation, soreness and blistering of surrounding skin. Fluorouracil cream is often used if someone has a large number of solar keratoses.
  • Imiquimod cream (brand name Aldara®) is an alternative. It is usually applied three times per week for a month initially. After a four-week break, the response of the skin treated is reassessed. Sometimes it is necessary to repeat one further four-week course. Imiquimod may also cause inflammation, irritation or redness of the skin where it is applied.
  • Salicylic acid ointment is another cream that is sometimes used. It may be used alone or as a pre-treatment before fluorouracil.

Photodynamic therapy

Photodynamic therapy is an alternative to topical treatments. It is used in conjunction with a cream called methyl-5-aminolevulinate (Metvix®). This cream is photosensitive (sensitive to light). A special light is then focused on the area to be treated. The combination of the cream and the light helps to kill the abnormal cells. This form of treatment may be useful if there are a large number of solar keratoses, or if the keratoses are around the eyes or where healing of the skin may be more difficult (such as the lower part of the leg). It may also be used if other treatments have not been successful.

Other treatments

A solar keratosis may be cut or scraped off. This are usually done after numbing the skin with some local anaesthetic. Other treatments which are sometimes used can include laser surgery, chemical peels and dermabrasion (where skin surface is removed by abrasion.)

Other risks if you have a solar keratosis

If you have one or more solar keratoses it is a marker that you have had a lot of sun exposure. The more serious type of skin cancer, melanoma, most commonly occurs in people who have had a lot of sun exposure. So, although a solar keratosis does not progress into a melanoma, if you have a solar keratosis, your risk of developing a melanoma on some other part of your skin is increased. So, tell a doctor soon if you notice any changes on any part of your skin, such as new moles, small dark patches developing, or a change in an existing mole (for example, if it is getting bigger, has an irregular outline, or is bleeding or crusting).

Can solar keratoses be prevented?

If you spend a lot of time in the sun you have an increased risk of developing solar keratoses and skin cancer. You will also prematurely age your skin and cause wrinkles.

To reduce the risk of developing skin cancers, solar keratoses and other conditions associated with sun-damaged skin, we should all:

  • Stay out of strong sunlight. In particular, avoid sun between 11 am and 3 pm.
  • When out in the sun:
    • Seek natural shade in the form of trees or other shelter.
    • Wear clothes as a sunscreen, including T-shirts, long-sleeved shirts, and hats.
    • Use a broad-spectrum sunscreen with an SPF of 30 or higher to protect against UVB and UVA.
    • Reapply sunscreen regularly, particularly if you are swimming, sweating a lot or after towelling yourself dry.
    • Use plenty of sunscreen. At the very least, six full teaspoons are needed to cover the body of an average adult.

It helps to examine your skin regularly. See your GP about any skin rashes, growths, lumps or bumps that do not heal within six weeks.

Further information

British Association of Dermatologists

Have a useful sunscreen factsheet, which includes answers to commonly asked questions about tanning, and explains the meaning of labels such as SPF, UVA and UVB star system. There are also information leaflets on skin cancers and actinic keratoses.
Web: www.bad.org.uk//site/734/default.aspx

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