How to Tell the Difference Between a Boil and a Cyst
Medically reviewed by Susan Bard, MD
Although they can look and feel similar, there are differences between a boil and a cyst. A boil is a pocket of pus caused by a bacterial infection of a hair follicle that tends to develop quickly. A cyst is an encased sac of fluid or tissue caused by many different things, which tends to develop slowly and can affect many different tissues, not just follicles.
Cysts and boils can be easily confused with each other. With a boil, the bump will be red, warm, tender, and swollen, while a cyst will usually be painless without redness or swelling. However, if a cyst ruptures and becomes infected, it can look and feel very much like a boil.
This article describes how a boil and a cyst differ in their symptoms, causes, and treatment.
What Are Boils and Cysts?
Boils and cysts may be similar in their presentation but are entirely different in why they occur.
A boil, also known as a furuncle, is a superficial pocket of pus that develops when bacteria get into a hair follicle. Pus is the aftermath of the body's immune defense, comprised of dead white blood cells, dead tissues, and dead bacteria. A carbuncle is a cluster of boils that extend into deeper tissues which can lead to the formation of an abscess.
A cyst is an encased sac of fluid or semi-solid materials that form in different tissues of the body. Those similar to boils are called cutaneous cysts, but cysts can also form in bones and muscles, in the reproductive tract, on organs, or in the central nervous system. Those affecting the skin can develop spontaneously, after an injury, or due to inflammatory or autoimmune diseases.
How to Tell the Difference Between Boil vs. Cyst
While both types of bumps can appear anywhere on your body, symptoms of a boil can vary from symptoms of a cyst. Knowing how each type of skin bump looks, feels, and affects your skin provides valuable clues when trying to identify a new bump on your skin.
Boils
A boil appears as a red to purple swollen skin lump, similar to a pimple. It usually has one or more whiteheads, called pustules, that form in the center. Pustules contain a white-yellow, pus-like fluid that may ooze from the boil.
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The size of a boil varies. It can range from the size of a cherry stone to the size of a walnut, and some grow even larger. The size of a boil may increase quickly as the pus increases within the boil. As the amount of pus increases, pain may become more intense.
A boil may feel tender to the touch or hurt constantly. You may notice itching at the site of the boil before it forms. Depending on the extent of the infection, you may also develop a fever and/or fatigue.
A boil usually appears in one of the following areas:
Face
Neck
Armpit
Thighs
Cutaneous Cysts
A cyst is a closed, saclike tissue pocket that forms under the skin. It usually contains keratin. There are many different types of cysts that can affect the skin or the underlying subcutaneous layer.
These cysts appear as smooth lumps that are whitish-yellow or the color of your skin. They can range in size from 1/2 inch to several inches across. A cyst is usually painless and may not require treatment.
Reproduced with permission from © DermNet New Zealand www.dermnetnz.org 2023.
A cyst is usually benign (noncancerous). It is painless and doesn't cause other symptoms unless it affects the normal function of the body system. Skin cysts usually appear in one of the following areas:
Scalp
Face
Trunk
Upper back
Groin area
Boil
Swollen, fast-growing red skin bump
Filled with whitest-yellow colored pus
Painful to the touch and/or constantly sore
White or yellow head filled with pus
Possible fatigue and/or fever
Cutaneous Cyst
Round, slow-growing skin bump
Filled with a yellow, foul-smelling keratin
Swollen, warm to the touch, painless
White or yellow color with a blackhead
No related fever or fatigue
Learn More: When to Worry vs. Not Worry About Lumps Under Your Skin
Causes of Boils vs. Cysts
The causes of a boil and a cyst differ. A boil is caused exclusively by a bacterial infection, while cutaneous cysts commonly develop when skin cells are not properly shed.
Boils
A boil develops from an infection of a hair follicle and the surrounding tissue. The most common source of infection is a staph infection caused by the Staphylococcus aureus (S. aureus) bacterium. The infection causes the skin tissue inside the boil to die. Then, a pus-filled hollow space, called an abscess, develops within or just below the skin's surface.
Most people have S. aureus bacteria on their skin and in areas like the lining of their noses without boils recurring. Boils are more likely to develop in people with the following characteristics:
Weakened immune systems
Specific allergies like allergic asthma
A boil is contagious when a break in the skin and person-to-person contact with pus drainage and skin bacteria occurs. It may also spread from contact with contaminated surfaces and objects.
Cutaneous Cysts
The outermost layer of your skin, called the epidermis, slowly sheds skin cells to make way for new ones emerging from the lower layer of skin, called the dermis.
Cutaneous cysts form when skin cells are not shed as they should be and instead fold into themselves. This forms an encased sac filled with dead skin cells and fluid. When the cyst reaches a certain size, it usually stops growing.
Some of these cysts form because of skin damage, such as that caused by a body piercing.
There are different types of cutaneous cysts, including:
Epidermoid cysts that appear on body parts with little hair
Myxoid cysts that develop near toenails or fingernails
Pilar cysts that form on the scalp
Sebaceous cysts that form in blocked sebaceous glands
Is It Possibly a Pimple?
A pimple occurs when dead skin cells, excess oil, and bacteria get trapped inside a pore. As the bacteria multiply, they cause inflammation, and a pimple forms on the skin's surface.
A pimple is typically painless and smaller than either a boil or a cyst. It usually grows no larger than the size of a dime and does not increase much in size after it erupts.
While a pimple often occurs in clusters, a cyst or boil usually appears as a single lump. Unlike a cyst or boil, a pimple may be a sign of acne, a chronic condition that recurs despite treatment.
Diagnosing Boils vs. Cysts
Only a healthcare provider can make an accurate diagnosis of your skin bump. Your healthcare provider may be able to recognize a boil or cyst based on the appearance of the bump and a description of your symptoms.
Factors such as when you first noticed the bump, how quickly it grew, whether it has changed in size, and if it is painful can help make a diagnosis.
Depending on the symptoms of your skin bump, your healthcare provider may perform the following laboratory tests. These tests may be performed if you often get boils, have several boils at the same time, or have a high risk of complications from a boil or cyst:
A tissue sample (scraping or biopsy of a cyst to identify an infection, benign tumor, or cancer)
Blood tests to identify whether the infection has spread
Pus swab to find out the type of bacteria causing the infection and which antibiotics will work best
Learn More: My Doctor Ordered a Bone Marrow Biopsy: What Happens Next?
How Do You Treat Boils vs. Cysts?
A boil or cyst can sometimes heal on its own without treatment or be managed at home with simple, self-care remedies. However, if the lump is causing excessive pain or discomfort, you may need to seek care from a skin specialist known as a dermatologist.
The one thing you should never do to do is squeeze a boil or cyst. The American Academy of Dermatology (AAD) warns that squeezing a boil can force pus into deep tissues, increasing the risk of an abscess or a deeper infection known as cellulitis.
Similarly, squeezing a cyst can rupture tissues and make way for a potentially severe secondary bacterial skin infection.
Boils
If you have a boil, there are several steps you can take to ease pain and encourage the drainage of pus from the skin:
Soak a clean cloth in warm water and hold it against the boil for 10 minutes four times a day. The moisture can loosen any crusting at the opening of the follicle, while the warmth encourages the dilation (opening) of the pore.
If pus comes out, clean the skin with water and antibacterial soap to prevent any further spread of infection. Wash your hands afterward as well.
Cover the area with a dressing or gauze until it heals.
Take Tylenol (acetaminophen) or Advil (ibuprofen) to help ease the pain.
Do not pick at the skin to loosen any scabs or share towels or other personal items that may have pus on them.
If a boil fails to respond to home treatment after two weeks, you should seek care from a dermatologist. The dermatologist can lance (cut open) the boil under sterile conditions to allow pus drainage. Antibiotics may be prescribed if the boil is large, recurrent, or in parts of the body where bacteria accumulate (such as the groin, breasts, armpits, or around the nostrils).
Cutaneous Cysts
Strictly speaking, cutaneous cysts are not treated at home. Unless the cyst is infected, treatment with warm compresses will do little, if anything, to resolve the condition. If a cyst causes pain and inflammation, Advil and/or ice application for 10 to 15 minutes is more likely to provide relief.
There is some evidence that certain natural tinctures can reduce epidermoid cysts. A 2020 study in Integrative Medicine reported that a topical tincture comprised of Calendula officinalis (pot marigold), Echinacea, Hydrastis canadensis (goldenseal), and Centella asiatica (gotu kola) was able to reduce a cyst in a patient after two months of daily treatment.
Failing this, treatment by a dermatologist may be needed if a cyst is causing pain, getting larger, or is unsightly. The treatment would involve the surgical removal of the mass under local anesthesia. Depending on the size and location of the cyst, this may involve surgical excision (using a scalpel) or CO2 laser excision. Most excisions can be done in the provider's office.
When to See a Healthcare Provider
You should seek medical care if a boil or cyst causes pain or is getting bigger. A larger concern is when a cyst becomes infected or a boil suddenly starts affecting deeper tissues.
With this in mind, contact your health provider if you develop the following signs or symptoms:
Fever with chills
Increasing pain, redness, heat, or swelling of cyst or boil
A foul-smelling discharge
Rapidly expanding red streaks on the skin
Preventing Boils vs. Cysts
You may be able to prevent boils by taking the following precautions:
Avoid wearing tight clothing that can cause friction on the skin and cause a hair follicle to swell up, starting an infection.
Wash boil-prone areas with soapy water often.
Wash your hands frequently, especially after touching or treating a boil.
Avoid sharing personal items like towels, bedding, or razors to prevent the spread of infection.
There is no known technique for preventing skin cysts. However, you can prevent potential infection and scarring of a cyst if you avoid squeezing, popping, lancing, or trying to drain the cyst yourself. Doing this increases the risk of inflammation or infection.
Summary
Boils and cysts are two common types of skin bumps. They can look alike even though their causes differ.
A boil is caused by a bacterial infection that affects a hair follicle and the tissue around it. A cyst occurs when skin cells grow and then can't reach the surface and become blocked below the skin.
While both skin lumps may heal without treatment, home care or surgery to remove the boil or cyst may be needed. Treatment for a boil can involve using antibiotics to treat the infection. A cyst usually doesn't need treatment unless it causes pain or prevents you from doing normal tasks.
Proper handwashing is one way to reduce the risk of boils and the spread of infection that occurs with them. There is no known way to prevent a cyst. Removing the cyst prevents it from recurring.
Read the original article on Verywell Health.
