Do I Have A Boil Or A Cyst How To Tell The Difference?

You felt a lump under your skin and now you are trying to figure out what it is. The short answer is that boils are infected hair follicles that fill with pus, while cysts are non-infectious sacs filled with fluid or other material. Boils are usually red, painful, and warm to the touch, while cysts often feel firm or rubbery and are not typically painful unless they become infected. This guide will help you tell the difference based on appearance, symptoms, and what doctors look for.

What is a Boil Exactly?

A boil, also known as a furuncle, starts as a bacterial infection in a hair follicle. The most common cause is Staphylococcus aureus bacteria. When the follicle gets infected, your body sends white blood cells to fight it. This creates a pocket of pus under the skin.

Boils usually appear quickly, over a few days. They start as a red, tender bump and grow larger. The skin around a boil is often red and swollen. As the boil develops, it fills with pus and forms a white or yellow tip. You may also have a low-grade fever or feel run down.

Boils are common on areas where skin rubs together or sweats heavily. This includes the neck, face, armpits, thighs, and buttocks. The CDC reports that boils are one of the most common skin infections seen in outpatient clinics. They are contagious through direct contact with the pus or through shared items like towels or razors.

What is a Cyst Exactly?

A cyst is a closed sac under the skin. It is usually not caused by an infection. Most cysts form when a skin cell or oil gland gets trapped under the surface. The sac fills with a soft, cheese-like material called keratin. This material is made of old skin cells and oils.

Epidermoid cysts are the most common type. They often appear on the face, neck, back, or torso. These cysts grow slowly and can stay the same size for years. They feel smooth and round, like a small marble under the skin. You can often move them slightly with your fingers.

Unlike boils, cysts are not usually red or painful. They are not contagious. However, a cyst can become infected if bacteria enter through a break in the skin. When that happens, it looks and feels a lot like a boil. Research published in the Journal of the American Academy of Dermatology notes that up to 30% of cysts eventually become infected or inflamed.

Do I Have A Boil Or A Cyst How To Tell The Difference

The table below summarizes the key differences. Use this as a quick reference, but remember that only a doctor can give you a definitive diagnosis.

What Causes These Lumps and Who Gets Them?

Boils happen when bacteria get into a hair follicle. This is more likely if you have a cut, scrape, or insect bite near the area. People with diabetes, weakened immune systems, or skin conditions like eczema get boils more often. The American Academy of Dermatology states that recurrent boils are sometimes linked to carrying Staph bacteria in the nose or on the skin without getting sick.

Cysts form for different reasons. Epidermoid cysts are often linked to genetics. If your parents had them, you are more likely to get them. Pilar cysts, which form on the scalp, also run in families. Some cysts form after an injury to the skin, like a deep scratch or surgery. Acne can also lead to cysts when oil and dead skin cells block a pore deep under the surface.

Both boils and cysts become more common with age. Hormonal changes, like those during puberty or pregnancy, can increase oil production and raise the risk of cysts. Poor hygiene does not directly cause either condition, but it can increase the risk of infection in existing cysts or minor skin injuries.

When Should You See a Doctor?

Most boils heal on their own within one to two weeks. You can try warm compresses three to four times a day to help the boil drain naturally. Never squeeze or pop a boil yourself. This can push the infection deeper into your skin or into your bloodstream, which can be dangerous.

See a doctor if a boil does not drain after two weeks, if it is larger than a ping-pong ball, or if you have a fever. Also see a doctor if you get boils over and over again. This may indicate a deeper infection or a carrier state of Staph that needs treatment. Doctors can drain a boil safely and may prescribe antibiotics if the infection is severe or spreading.

Cysts rarely need treatment unless they bother you. You can leave a cyst alone if it is not painful and not growing. See a doctor if a cyst becomes red, swollen, or painful. This means it is likely infected. A doctor can drain the cyst and remove the sac wall to prevent it from coming back. If you are worried about a cyst on your face or another visible area, a dermatologist can remove it for cosmetic reasons.

There is one situation where you should see a doctor immediately. If you have a red streak extending from the lump, or if you have a fever above 101°F (38.3°C) with chills, go to urgent care or the emergency room. These are signs of a spreading infection called cellulitis, which can become serious quickly.

Common Misconceptions and What to Avoid

There is a lot of bad advice online about treating skin lumps. Some people say to put toothpaste, tea tree oil, or garlic on a boil or cyst. There is no clinical evidence that any of these work. In fact, some can irritate the skin and make the problem worse. The American Academy of Dermatology specifically advises against using home remedies that are not backed by research.

Another common myth is that boils are caused by “bad blood” or poor diet. This is not true. While a healthy diet supports your immune system, boils are caused by bacteria, not by what you eat. Similarly, cysts are not caused by toxins or a need to “detox.” They are structural issues with your skin.

Avoid trying to drain a cyst at home. You can easily introduce bacteria and cause a serious infection. Even if you manage to drain it, the sac wall often stays behind. This means the cyst will fill up again. Doctors remove the entire sac wall to prevent recurrence. For boils, never use a needle or blade to open them yourself. The risk of infection is too high.

Some people believe that all lumps under the skin are cancerous. This is not true. The vast majority of boils and cysts are benign. Skin cancer rarely looks like a boil or cyst. However, any new or changing lump should be checked by a doctor. If a lump is hard, irregularly shaped, or growing rapidly, a biopsy may be needed to rule out cancer. This is rare, but it is worth mentioning to your doctor.

How Doctors Diagnose Boils and Cysts

Diagnosis is usually straightforward. A doctor will look at the lump and feel it. They will ask about your symptoms, how fast it grew, and if you have had one before. In most cases, that is all that is needed.

Sometimes a doctor uses a tool called a dermatoscope. It is a magnifying lens with a light. It helps them see details on the skin surface that are not visible to the naked eye. For example, a cyst often has a small opening called a punctum on the skin above it. This is a key sign that helps distinguish it from a boil.

If there is pus, a doctor may send a sample to a lab. This is called a culture. It identifies the exact bacteria causing the infection. This is most useful for people who get boils often. The lab can also test which antibiotics will kill the bacteria. This helps doctors choose the right treatment.

Imaging is rarely needed. An ultrasound can show if a lump is solid or filled with fluid. This is sometimes used if the diagnosis is unclear. CT scans or MRIs are almost never used for boils or cysts. They are reserved for very deep lumps that might be something else, like a tumor.

What About Recurring Boils or Cysts?

Some people get boils over and over again. This is called recurrent furunculosis. It can be frustrating and painful. The CDC estimates that about 2% of the general population has recurrent boils. If this happens to you, your doctor may check for underlying conditions like diabetes or a weakened immune system. They may also test if you are a carrier of Staph bacteria.

For carriers, treatment may include a special antibiotic ointment applied inside the nose and using antibacterial washes on the skin. This can reduce the amount of bacteria on your body and lower the risk of new boils. Good hygiene, like frequent hand washing and not sharing towels, also helps.

Recurring cysts are less common. If a cyst keeps coming back after being drained, it usually means the sac wall was not fully removed. The only way to prevent a cyst from returning is to have the entire sac surgically removed. This is a minor procedure done in a doctor’s office under local anesthesia.

Some people have a genetic condition called Gardner syndrome that causes many cysts. This is rare. If you have multiple cysts, especially on your scalp or back, mention it to your doctor. They can check if there is an underlying condition that needs attention.