Home . News . Where to donate . What happens . Who can donate . How to enrol . All about blood . About the NBS . How to help . Contact the NBS . Site map . Fun zone  Feeling faint Donating blood is simple Apheresis donation Donor card scheme FAQs Where your blood goes Your Donation Feeling Faint Occasional Bruising Bone Marrow Donation Feeling faint What follows in this section is the official medical stance on why some people might possibly feel a bit faint after a donation session: It is important to be aware that some donors feel faint after giving blood. During blood donation 8-10% of your blood volume is removed. Most people adapt quickly to this loss and their system is not upset by it, but a few individuals adapt less well and consequently feel faint. The effects of the removal of a unit of blood are aggravated by various factors: People who weigh less than 7st 12lbs (50kg) are more likely to faint if they give blood because they lose relatively more of their blood volume than larger people. Therefore we advise them not to donate, in the interests of their own health and well-being. People who smoke soon after giving blood are more likely to feel the effects of nicotine and therefore faint. People who take alcohol within a few hours of giving blood are more likely to feel faint because alcohol dilates the blood vessels. This causes less blood to be available to circulate to the brain leading to dizziness and fainting. Being in a hot room also causes the blood vessels to dilate and thus has a similar effect to alcohol. Rushing about, or vigorous exercise can also produce similar effects. Missing meals and not replacing fluids means a delay in the recovery from blood donation. Standing still for long periods of time can lead to pooling of blood in the legs, a situation similar to soldiers on parade. This reduces the amount of blood available to the brain. If you rush about, miss a meal, have a 'liquid lunch', a cigarette, or get overheated you may feel faint even if you gave blood several hours ago. If you feel faint it is important to: tell someone, either a friend or a member of our staff if you are at a session. THEN lie down, or bend forward with your head between your knees until the feeling passes. Make sure that when you get up you do so slowly. If you still feel faint, lie down again. Feeling faint can happen to anyone. However, fainting can often be avoided by following the advice given to you by the National Blood Service. The main considerations are: follow the advice about resting after your donation. take plenty of fluid. do not smoke or drink alcohol within 2 hours of giving blood. avoid rushing around, standing still, hot environments and vigorous exercise. With these general measures, donors can minimise the chances of fainting. If any problems persist you can obtain advice by ringing our Donor Helpline on 0845 7 711 711 as soon as possible. View Current Blood Stocks   Shaun's story Privacy & Legals notice  RETURN TO TOP OF PAGE