Boil, Pimple or Cyst? How to Tell the Difference

The quick answer

The difference comes down to where the bump starts. A pimple starts in a clogged pore. A boil starts when bacteria infect a hair follicle.² A cyst is a small sac under the skin that slowly fills up.⁴

That’s why they behave so differently. Pimples come and go. Boils tend to get bigger and more painful over a few days. Cysts can sit quietly for months. Here’s what to look for with each one.

Knowing which one you have matters. A boil is a bacterial infection and sometimes needs a doctor to drain it.² A cyst, on the other hand, can swell and hurt without being infected at all.⁴

Pimples: a clogged, inflamed pore

Pimples are a type of acne. They form when extra oil, dead skin cells and bacteria get trapped inside a pore, and the area becomes inflamed.¹ Whiteheads and blackheads are the milder versions: pores plugged with oil and dead skin.¹

Acne is common on the face, but it can also appear on the back, chest, neck, shoulders, upper arms and buttocks.¹ When the inflammation goes deep into the skin, it can form a hard acne nodule or a softer, pus-filled acne cyst.¹ These deep breakouts can feel a lot like a boil, which is one reason people mix them up. A dermatologist has in-office treatments that can flatten most deep acne bumps within a few days, so there’s no need to wait them out in pain.⁵

Boils: an infected hair follicle

A boil, also called a furuncle, is a pus-filled bump that forms when bacteria infect a hair follicle. It is usually caused by Staphylococcus aureus, or staph.²

Clues that you’re dealing with a boil:³

• It starts as a small, painful red bump and gets bigger, sometimes more than 2 inches across.
• The skin around it is red or purplish and swollen.
• Over a few days, a yellow-white tip forms and may break open and drain.
• It tends to show up on the face, neck, armpits, thighs or buttocks.

A cluster of boils joined under the skin is called a carbuncle. It is deeper, more likely to scar, and can come with fever and chills.³ If boils keep returning, read why boils keep coming back.

Cysts: a slow, quiet sac under the skin

A common type of skin cyst is the epidermoid cyst. It’s a small, round bump under the skin, often on the face, neck or trunk. Some have a tiny blackhead plugging an opening in the center.⁴

Epidermoid cysts grow slowly and are often painless.⁴ If one breaks open, a thick, cheesy, bad-smelling material can leak out. That material is mostly keratin, a protein your skin makes.⁴ A cyst can also turn painful and swollen even when it isn’t infected.⁴

Side by side: quick clues

No checklist replaces a doctor’s exam, but these differences can help you describe what you’re seeing:

• Speed: a boil usually grows and gets more painful over a few days; a cyst tends to grow slowly.³⁴
• Pain: boils are painful from the start; many cysts don’t hurt unless they become inflamed.³⁴
• Center: a boil forms a yellow-white tip; a cyst may have a tiny dark dot.³⁴
• Surrounding skin: a boil usually has red or purplish swelling around it.³
• Company: pimples usually show up with other acne nearby, such as blackheads and whiteheads.¹

Why you shouldn’t squeeze any of them

Whatever the bump is, leave it alone. Squeezing a pimple can push its contents deeper into the skin, which increases inflammation, and bacteria from your hands can cause an infection. It also raises the risk of scars.⁵ Squeezing or lancing a boil can spread the infection.⁶

Dermatologists have safer options, including draining a bump with sterile tools when it needs it.⁵ For more on boils, see should you pop a boil?

When to see a doctor

See a doctor or dermatologist if a bump:³⁴

• Gets bigger quickly or is extremely painful
• Comes with a fever or chills
• Is on your face or affects your vision
• Hasn’t healed in two weeks, or keeps coming back
• Is a cyst that grows fast, breaks open or looks infected

If you have diabetes or a weakened immune system, don’t wait on any painful, red bump. Get urgent care or call 911 for fever with fast-spreading redness, confusion or feeling very unwell.