What is a solar keratosis?

A solar keratosis is a small, thickened, scaly growth (or lump) which develops on the skin. It is caused by a lot of exposure to the sun over many years. One or more may develop. It is sometimes called an actinic keratosis.

What does a solar keratosis look like?

Who gets solar keratoses?

Solar keratoses are caused by damage to the skin by ultraviolet light which is part of sunlight. The skin is normally pretty 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. Because their skin has less protective pigment, they are the most susceptible to sunburn and other forms of sun damage. As it usually takes years of sun exposure to develop a solar keratosis, older people tend to be most commonly affected. But, they may appear at a much earlier age in people who work outdoors, or who do a lot of sunbathing or use sunbeds frequently.

Solar keratoses are more common in people who have had long-term treatment to suppress their immune system, such as people who have had organ transplants. However, even in such people, they do not occur without exposure of the skin to the sun.

Are solar keratoses dangerous?

In themselves, solar keratoses are not cancerous and do no harm. But, they can sometimes be unsightly. Also, 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 over a 10 year period. This is not the most serious form of skin cancer. It is a fairly slow growing cancer and can usually be easily cured if treated early enough.

How are solar keratoses diagnosed?

Your doctor may be able to diagnose a solar keratoses by its typical appearance alone. However, sometimes this may be difficult. You may be referred to a dermatologist and/or your doctor may suggest that a skin biopsy is taken. This is where a small sample of your skin is taken and examined under the microscope in a laboratory.

What is the treatment for solar keratoses?

No treatment may be an option

Without treatment up to a quarter of solar keratoses will clear away 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 cream to help soften the skin around the solar keratosis. Alternatively, you may be advised to apply sun cream with a high sun protection factor. This can also help to soften and moisturize the skin as well as protecting the skin from the sun and against the development of further solar keratoses.

If treatment is advised, a number of different methods may be used. The method that your doctor may advise can depend on things such as the number of solar keratoses that you have, where they are and how big or thick they are. Your health and your preference may also be taken into consideration.

Freezing a solar keratosis with liquid nitrogen

This is a common treatment in people who have small numbers of solar keratoses. This 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

This option is sometimes used, especially if you have a lot of small solar keratoses where you would otherwise need repeated freezing to get rid of them all.

• One type of gel contains an anti-inflammatory drug called diclofenac. This may take up to 3 months or more of treatment to clear the skin. Side effects may include itching and a rash.
• Another cream which is sometimes used contains a drug called 5-fluorouracil. This kills the abnormal cells and fresh normal skin grows back. This cream is usually applied for between 3-6 weeks but it can cause quite a lot of inflammation, soreness and blistering of the surrounding skin for a while. 5-fluorouracil cream is often used if someone has a large number of solar keratoses.
• Imiquimod cream is an alternative. It is usually applied for one month initially but longer courses may be needed. It 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 5-fluorouracil.

Photodynamic therapy

This is another type of treatment that may be suggested. First a special cream is applied to the skin that 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 in areas 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 keratosis 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, etc.

Can solar keratoses be prevented?

If you spend a lot of time in the sun you have an increased risk of developing solar keratoses, certain types of skin cancer and various other skin problems. So, to reduce the risk of developing these conditions we should all:

• Stay out of strong sunlight. In particular avoid sun between 11am and 3pm.
• 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 sun screen with a sun protection factor (SPF) of 30 or higher to protect against UVB and UVA.