Treatments such as creams used on the skin are known as topical treatments. Most topical treatments go no further than the skin. They aren't absorbed into the body but stay in the surface layers. So the drugs in them don't reach the rest of the body.

However, there are some drugs - including steroids - that do penetrate and reach the bloodstream when given topically. They're then carried around the body. So, topical steroids can have effects both in the skin and elsewhere in the body.

Why are topical steroids used?

Cream or ointments containing steroids are often used to treat skin conditions in which there seems to be inflammation, even if the exact diagnosis of the problem isn't clear.

If there's a possibility of infection, then an antibiotic or antifungal drug must be included in the cream. (Steroids alone shouldn't be used when there's a risk of infection because the drugs lower immunity and could allow infection to spread rapidly.)

Steroids are powerful anti-inflammatory drugs. They prevent the release of chemicals which trigger inflammation. They're used for conditions such as eczema, dermatitis and psoriasis. These usually improve rapidly when steroids are started.

The risks vary

Weaker steroid creams rarely cause side effects, and doctors are so confident about their use that they can even be bought over the counter without a prescription.

But the stronger the steroid within the cream, the greater the risks. These risks increase the longer the cream is used. For this reason, high-strength steroid creams can only be used on prescription, often for a limited period.

Side effects on skin

Prolonged use of potent steroids can cause permanent changes to the skin. These include:

• Thinning of the skin
• Stretch marks
• Development of fine blood vessels in the skin (telangiectasia)
• Easy bruising
• Loss of pigmentation in darker skins

Because of these changes, steroid creams are rarely used on the face, especially in high concentrations.

General side effects to the whole body

Prolonged use of topical steroids can occasionally cause more general problems, known as systemic side effects. These include:

• Roundness of the face ('moon face')
• Central obesity
• Fat pads on the back and neck
• Acne
• Mood changes
• Osteoporosis
• Peptic ulcers
• Raised blood pressure
• Abnormal insulin and sugar metabolism
• Reduction in immunity (with an increased risk of infection)

These features are sometimes called Cushing's syndrome.

Follow instructions closely

Use steroid creams only as directed by your doctor. It's safe to finish one prescription but don't go on using them by, for example, buying weaker steroid creams in the pharmacy without talking first to your doctor.

It may be safe to go on using steroid creams for some weeks and months, especially if you're only applying it to a small area and not giving yourself much of a dose.

In some conditions, such as severe eczema, the risks of long-term use of steroid creams may be worth the relief from the condition, and it's simply necessary to be vigilant for any problems.

This article was last medically reviewed by Dr Trisha Macnair in July 2008