Platelets are tiny bits of cells that help to stop bleeding. During chemotherapy the numbers of platelets in your blood can fall. If the levels drop too low you may be given a platelet transfusion to stop you having problems with bruising or bleeding.

Platelets are made in the bone marrow and circulate in your blood. They help to stop bleeding at places where blood vessel walls are damaged. There are normally between 150 and 450 million platelets in every millilitre of your blood. They usually last for about 10 days before they are used up.

When a blood vessel is damaged platelets rush to stick to the injured area and form a clump. They bind tightly and release lots of different chemicals. These chemicals do many different things. Some narrow the blood vessel, to reduce the amount of blood that is lost. Some attract more platelets, to make the clump bigger. Some activate clotting factors, which lay down fibres (fibrin) around the clump. This holds everything together to form a blood clot. You see this as a scab after you cut yourself.

When your bone marrow is not working, because of illness or chemotherapy, your platelet count drops. Most of the time having a slightly lower platelet count doesn't cause you any problems. But, if it is very low (below 10 million in every millilitre of blood) this can be more dangerous. You might have nosebleeds, bleeding gums, heavy periods or tiny, round red spots under your skin caused by bleeding (petechiae). There is also a risk that you could bleed into your brain, stomach or bowel. But, fortunately this complication is rare because people are given platelet transfusions if their counts are very low.

Your doctors will check your blood counts regularly so that if your platelet count is too low you can be given a platelet transfusion. But, if you feel unwell or notice any unusual bruising or bleeding in between these checks let your doctor know.