Cysts and boils both cause lumps to form under the skin. They are often similar in appearance, but their causes and treatment are not the same.
A cyst is a small fluid-filled lump that can form in or on a person's body. It can be easy to confuse a cyst with a boil as they may have similar symptoms.
According to the American Osteopathic College of Dermatology (AOCD), there are three types of common skin cyst:
- epidermal cysts
- trichilemmal cysts
Epidermal and trichilemmal cysts look very similar to each other, but the latter mostly occur on a person's scalp. Milia cysts are smaller and tend to occur more on the face, especially around the eyes.
Cysts are usually benign, which means that they are noncancerous.
According to the National Centre for Biotechnology Information, bacterial infections are responsible for causing boils, which are pus-filled lumps under the skin that form around hair follicles.
Skin cysts and boils can present in a similar way, but they are not the same.
According to the AOCD, a person can move an epidermal cyst under their skin. Skin usually covers the cyst, but it may sometimes have a central pore. Cysts range in size from 0.5 to several centimeters.
A person will not usually notice any symptoms alongside their cyst. However, if the cyst ruptures or gets infected, it may become red, swollen, and painful, closely resembling a boil.
A person is most likely to get boils on their face or neck, but they can also appear:
- in the armpits
- around the groin, including the genitals
- on the thighs
- on the bottom
Despite their similar appearance, there are important differences between cysts and boils.
If a person has a cyst without inflammation, they may not experience any associated symptoms, but if the cyst does become inflamed, it may be red, swollen, and painful.
A cyst can rupture on sudden exposure to pressure, for example, if a person falls on it. If it does burst, a person may notice yellow, unpleasant-smelling pus.
It is not clear exactly why people get cysts, but they form when skin cells quickly multiply.
Gardner's syndrome and Gorlin's syndrome can cause a person to develop cysts. These lumps may also have an association with sun damage to a person's skin, and some medications might increase the likelihood of a cyst forming.
Cysts can also appear after a person sustains damage to their skin, although the underlying cause is often not clear.
Treatment for a cyst usually involves minor surgery to remove it. A doctor will give the individual a local anesthetic before removing the whole of the cyst, making as small an incision as possible to try to prevent scarring.
Unlike most cysts, boils are swollen, red, and sore. People may see yellow pus in or on the boil. A boil may make a person feel weak or tired if they develop a fever because of the bacterial infection.
Boils usually occur as a result of bacterial infection around a hair follicle. This infection causes the surrounding skin cells to die, and pus then replaces them. Sometimes, several boils will develop in a cluster, which is called a carbuncle.
Although bacteria are the underlying cause of boils, antibiotics are not usually the first treatment for a boil unless it is severe or many boils have formed.
People can often treat boils at home. The American Academy of Dermatology recommend applying a warm, damp, clean cloth to the boil. Doing this encourages the boil to release its pus, which helps it heal. Ibuprofen, available over the counter or online, can help relieve pain and inflammation.
A person should not squeeze a boil as this may worsen the infection.
If a boil is severe or persistent, a doctor might take a sample of the pus in the boil and send it to a laboratory to determine which bacterial infection has caused it. When they know which bacteria are responsible, the doctor can prescribe the most effective antibiotic to fight the infection.
Although cysts and boils may look similar, especially if a cyst becomes inflamed, there are important differences between them.
Cysts are not generally painful, but most boils are sore. Boils tend to be a little larger than cysts and appear red and swollen. Doctors can treat cysts with minor surgery, whereas people can usually treat a boil at home.
In either case, if a person's cyst or boil causes any unusual symptoms or does not resolve, a medical professional can provide advice.