To understand how corticosteroids work, it is useful to know about the processes in the body that cause inflammation.

Inflammation

If part of your body becomes infected, your immune system (the body’s natural defence against infection and illness) responds by flooding the area with infection-fighting antibodies.

The antibodies limit the spread of infection and kill off the virus, bacteria or fungus that is responsible for it. However, in the process, the affected area will become swollen, warm and, in the case of the skin, red. This is known as inflammation.

Inflammation is usually useful in helping prevent the spread of infection. However, sometimes the immune system malfunctions, causing inflammation even though no infection has occurred. This is what happens in conditions such as rheumatoid arthritis, which are known as autoimmune conditions. Alternatively, the immune system may mistake harmless substances, such as pollen or dust mites, for a threat and trigger an allergic reaction.

Corticosteroids work by blocking the effects of some chemicals that the immune system uses to "kick-start" the process of inflammation. They can also disrupt the normal functions of white blood cells, which the immune system uses to target and destroy infectious agents such as viruses and bacteria.

However, the disadvantage of corticosteroids is that they make you more vulnerable to infection.

Read more about the side effects of corticosteroids.

Types of corticosteroid

Some commonly prescribed types of corticosteroid include:

• hydrocortisone – usually used as a cream or lotion, hydrocortisone injections are sometimes used to relieve inflammation in joints and tendons
• prednisolone – available as a tablet, injection or as a suppository (a tablet you put in your back passage), prednisolone is used to treat a wide range of autoimmune and allergic conditions
• dexamethasone – usually given by injection, dexamethasone is often used when there is an urgent need for treatment, such as when there is swelling in the brain due to a brain tumour or someone is having serious breathing problems due to an allergic condition
• fludrocortisone – this type of corticosteroid is mainly used to treat Addison’s disease, a condition where the body does not produce enough naturally occurring steroid hormones