WebMD explains that a blood-filled pimple is most likely a form of cystic acne, which means that it goes much more deeper into the skin than a regular pimple. Acneic cysts take quite a while to heal and are very painful. They are usually a dark, brownish red color due to the strong presence of blood that collects under the surface of the skin.
Unlike regular pimples, acneic cysts are not easily popped. WebMD strongly advises against attempting to drain the fluid from a cyst, as many eventually heal on their own without ever coming to a head. Cysts usually do not protrude from the skin as much as other pimples do, and attempting to pop them conventionally is likely to push the infection deeper and cause internal bruising in the face. Cysts do not form white heads containing pus, which is what most people are familiar with from common pimples. Cysts also do not seem to respond well to treatments such as antibiotics or topical creams and ointments. It is generally believed that cysts result from hormonal imbalances, according to WebMD. The best thing to do is to leave the cyst alone without poking or prodding it and to visit a dermatologist to determine if hormonal therapy, such as birth control or spironolactone, is the right course of action.