How can one tell the difference between a cyst and a boil?
Cysts and abscesses (I’ll use the medical term for boils) are both lumps or masses which may occur almost anywhere in the body or on the skin. Cysts may become abscesses. The basic distinction between the two is that an abscess is by definition a localized bacterial infection, whereas a cyst is an uninfected, fluid-filled mass.
The abnormal collection of fluid or other material which makes up cysts occurs because the fluid produced by a gland or an organ cannot be secreted in the normal way and thus builds up. The most common ones are sebaceous cysts, which form in the skin from the tiny glands that secrete sebum, the oily material normally found on our skin. Whiteheads on the face are small sebaceous cysts, while larger ones are common anywhere on the skin surface, and especially on the scalp. Many sebaceous cysts have a small opening at the top, the outlet for the gland that has become cystic, and squeezing the cyst may force out the oily material through the opening. Cysts are rarely painful.
Other common sites where one finds cysts are the kidney, the liver and occasionally the brain. Most cysts in these locations are benign and do not need to be treated, but if they are numerous, as can occur in polycystic kidney disease, or if they press on another vital structure, as may happen with brain cysts, then they may cause serious problems.
Some cysts are formed in tumors. This occurs if the tumor cells secrete a fluid into the tumor where it cannot escape, creating a cyst. Ovarian cancers are particularly prone to be cystic, but cancers in some other tissues may also be. Kidney cancers can be cystic, and differentiating between a single benign cyst of the kidney and a kidney cancer can occasionally be a problem. When many cysts are present, as in polycystic renal disease, the distinction is easier.
Cysts may also be caused by some parasitic infections. T. solium, the pork tapeworm, can cause cysticercosis if a human ingests the worm’s eggs by eating contaminated food. The eggs migrate to muscle tissue or the brain, where they slowly grow and form cysts. A different parasite known as echinococcus tends to form cysts in the liver and lungs. These cysts may be quite large and last for many years without producing symptoms. In the brain, of course, they are much more likely to cause serious disease.
Abscesses are localized infections typically caused by staphylococci, which have a tendency to produce pus and not to spread through tissue. Cysts which become infected may become abscesses. This is most common on the face, in the armpits and the inner thighs, but sebaceous cysts may become infected and turn into abscesses anywhere on the skin surface.
Abscesses may also occur in other tissues and internal organs, but internal cysts, such as kidney or liver cysts, seldom become infected and therefore do not turn into abscesses. Instead, internal abscesses usually form as a result of a pre-existing infection in the organ — for example tubo-ovarian abscesses that follow infection in the Fallopian tubes — or by bacteria that have spread through the bloodstream from an infected heart valve or an infection elsewhere.
Abscesses cause pain and often fever or other signs of localized infection. They almost always require treatment, and will often require drainage. Internal abscesses usually have to be surgically removed or drained. Antibiotics alone are generally not effective in treating abscesses, since the antibiotic cannot easily diffuse into the pus of the abscess. In addition, staphylococci and other abscess-forming bacteria are increasingly resistant to most antibiotics. After an abscess has been drained, and a culture taken to see if the bacteria are sensitive, then an antibiotic may speed healing.
Small abscesses on the skin may heal with only hot soaks as treatment, and I regularly tell my patients who are prone to styes (small abscesses of glands in the eyelids), or who get frequent abscesses under the arms or on the thighs to start hot-soaking the area as soon as they are aware of the painful swelling. This simple treatment is surprisingly effective if started early, before the infection has had a chance to grow.