While boils typically resolve on their own and therefore have an excellent prognosis, there are special cases in which medical care should be sought when boils develop. Rarely, boils may spread or persist, leading to more widespread infections.
Any boil or abscess in a patient with diabetes or a patient with an underlying illness that can be associated with a weakened immune system (such as cancer, rheumatoid arthritis, etc.) should be evaluated by a health care professional. Additionally, many medicines, especially prednisone, that suppress the immune system (the natural infection-fighting system of the body) can complicate what would be an otherwise simple boil. Those who are taking such medications should consult their health care professional if they develop boils. (If you are not sure about your medications' effects on the immune system, your pharmacist may be able to explain to you which medicines to be concerned about.)
Any boil that is associated with a fever should receive medical attention. Increasing reddening of the nearby skin and/or formation of red streaks on the skin, the failure of a boil to "form a head," and the development of multiple boils are other symptoms that warrant a visit to a health care professional.
A "pilonidal cyst," a boil that occurs between the buttocks, is a special case. These almost always require medical treatment, including drainage and packing (putting gauze in the opened abscess to assure it continues to drain). Finally, any painful boil that is not rapidly improving should be seen by a health care professional.