Acne on arms and thighs, and inner thigh blackheads

Bumps on the arms and thighs are common, and several different skin conditions cause them. The rough little bumps on the backs of the upper arms are usually keratosis pilaris. Sudden spots on the legs after shaving or tight leggings are often folliculitis. And blackheads or painful lumps in the inner thigh can be an early sign of hidradenitis suppurativa, a skin disease that is worth catching early. This guide helps you tell these apart, explains what helps each one, and says when to see a dermatologist. It is part of Skinli's guide to body acne.

Skinli gives general education, and it is not a doctor. A dermatologist can tell these conditions apart by looking at your skin.

Four common causes

Condition	Where it shows up	What it looks and feels like
Keratosis pilaris	Upper arms, front of the thighs, buttocks	Tiny rough bumps, like goosebumps, skin-colored, white, red or dark
Folliculitis	Anywhere with hair, often under tight clothing or after shaving	Sudden spots, each with a red ring, may itch or hurt
Acne	Mostly face, chest and back, and sometimes arms, legs and buttocks	Blackheads, whiteheads, red and pus bumps
Hidradenitis suppurativa	Where skin touches skin: inner thighs, groin, armpits, buttocks	Deep, painful lumps that return, sometimes blackheads in pairs

The sources for each row are set out in the sections below.

Keratosis pilaris: the rough bumps on the upper arms

The American Academy of Dermatology (AAD) calls keratosis pilaris "a common skin condition, which appears as tiny bumps on the skin." It says "some people say these bumps look like goosebumps or the skin of a plucked chicken. Others mistake the bumps for small pimples." The bumps are "plugs of dead skin cells," and they appear "most often on the upper arms and thighs (front)." In teens and adults, the AAD adds the buttocks.

The NHS describes it as harmless, says the bumps can be skin-colored, red on white skin or darker on brown or black skin, and says it "is thought to run in families." People cannot catch it from someone else, the NHS says. The skin can feel dry and rough, "like sandpaper," the AAD says, and it often looks better in summer and worse in winter.

What helps

Treatment is optional. The AAD says you do not have to treat it, but treatment helps if the itch, dryness or look bothers you. Its home plan has three steps, used every day until the skin looks clearer:

1. Exfoliate gently with a washcloth, and avoid hard scrubbing, which "tends to irritate the skin and worsen keratosis pilaris."
2. Apply a keratolytic, a product that loosens dead skin cells. The AAD lists products with alpha hydroxy acids such as glycolic or lactic acid, a retinoid such as adapalene or retinol, salicylic acid or urea. Stop for a few days if the skin gets dry or irritated.
3. Moisturize after bathing and when skin feels dry, at least 2 or 3 times a day, with a thick oil-free cream or ointment. Creams with urea or lactic acid help.

More tips from the AAD and the NHS: keep showers short and warm, use a mild cleanser, skip self-tanner, and use a humidifier when the air is dry. The AAD says shaving or waxing skin with keratosis pilaris can cause more bumps.

The AAD says that if you see no change after 4 to 6 weeks, tell your dermatologist, and that "for many people, keratosis pilaris goes away with time," over many years.

Folliculitis: sudden spots on the legs and arms

Folliculitis is an infection of the hair follicles, the small openings each hair grows from. The AAD says it "usually looks like a sudden acne breakout," with a red ring around each spot, and that it can appear anywhere except the palms and soles. The bumps may itch, hurt or cause no feeling at all.

The AAD lists the ways follicles get damaged, and several fit the arms and thighs:

• Wearing tight clothing
• Skin rubbing against skin
• Shaving, plucking or waxing
• Hot, damp skin, such as tight clothing rubbing during a bike ride on a hot day
• An unclean hot tub, which can cause spots under the swimsuit 12 to 48 hours later

The AAD says folliculitis tends to go away on its own if you have a healthy immune system and stop what caused it. It suggests a warm compress at least 3 to 4 times a day, for 15 to 20 minutes each time, and a 30-day break from shaving, plucking or waxing when those caused it. See body acne or folliculitis for how to tell it from acne.

Acne on the arms and legs

True acne can form on the limbs. MedlinePlus says "acne commonly appears on the face and shoulders. It may also occur on the trunk, arms, legs, and buttocks." If you have blackheads, whiteheads and red pimples on the arms along with acne on your face, chest or back, the usual acne products apply. The AAD suggests a retinoid such as adapalene and a benzoyl peroxide wash for blackheads and whiteheads, and a benzoyl peroxide or salicylic acid product for red and pus bumps. See acne body wash for how to use a wash on the body.

Blackheads and lumps in the inner thigh

The inner thighs deserve their own section, because this is where hidradenitis suppurativa, often shortened to HS, can start.

The AAD says HS "is a skin condition that causes painful lumps deep in your skin" that "usually develop on parts of the body where skin touches skin like the armpits, inner thighs, and groin area." Its first sign is often "a painful spot that looks like a deep pimple, acne cyst, or boil," and some people first get a spot on the buttocks or inner thigh. The AAD says HS is a different condition from acne, although many people with it first think they have pimples.

Blackheads can be part of HS. The NHS says HS "tends to start with blackheads, spots filled with pus and firm pea-sized lumps that develop in one place." The AAD says that in later stages, some people see "small black bumps that look like blackheads. These spots often appear in twos."

Other facts about HS from the AAD and the NHS:

• People cannot catch it from someone else, and the NHS says it has no link to poor hygiene.
• The NHS estimates it affects 1 in 100 people, more women than men, and says it usually starts around puberty.
• Lumps often clear for a while, then return in the same place.
• Without treatment it can form tunnels under the skin and scars. The AAD says treatment can prevent HS from getting worse.

If you have blackheads in pairs, or tender lumps that keep coming back in the inner thigh or groin, see a dermatologist. The AAD's self-care advice for HS includes looser clothing, no waxing, careful shaving, and a gentle antibacterial wash such as one with benzoyl peroxide. It also says to stop scrubbing, because "scrubbing causes inflammation, which can worsen HS."

Darker skin in the inner thighs

Some people search for dark inner thighs together with blackheads. The AAD's page on conditions that look like acne says that in polycystic ovary syndrome, a hormone condition, women often have acne along with "an area of skin that starts to darken and sometimes thicken," plus other signs such as extra facial hair or irregular periods. If you notice darkening skin along with acne and those signs, see your doctor.

What to do at home

• Wear loose clothing in hot weather, and change out of sweaty, tight clothes soon after exercise.
• Take a break from shaving or waxing areas with bumps.
• Wash gently with your hands, and skip rough scrubs.
• Moisturize dry, rough bumps if they look like keratosis pilaris.
• Leave bumps alone. The AAD says picking and popping make acne worse.

When to see a dermatologist

The AAD lists "pimple-like bumps in unusual places, such as your armpit, groin, thighs, or on the backs of your upper arms" as one reason to see a dermatologist. Go sooner if:

• You have deep, painful lumps, lumps that leak pus, or lumps that return in the same spot.
• You see blackheads in pairs in the inner thigh, groin or armpit.
• Folliculitis keeps coming back or spreads.
• Keratosis pilaris has not improved after 4 to 6 weeks of steady care.

Skinli's free acne plan is built for acne on the face from a photo, and it cannot assess the arms or thighs. For bumps lower on the body, see butt acne.