Dark Spots on Buttocks? Track Sitting Hours, Clothes and Scrubbing

Daily situation	Why you log it	Basis
Long hours of pressure from sitting	When skin is pressed or rubbed and sweat builds up, its defenses break down and boils form more easily	KDCA Boils (updated 2026) · agency
Scrubbing in the shower	On the side scrubbed with a nylon towel twice a day for 2 weeks, skin water loss went up (6 people)	2018 PMID 29243811 · B
Picking or scratching bumps	Named as a risk factor for dark marks after acne	2021 PMID 34880967 · B
Friction itself	Pigment changes caused by friction have their own name and have been studied (52 people)	2012 PMID 23248362 · B
How often to compare	Half or more of dark marks after acne last a year or longer → one photo a month	2016 PMID 26813513 · B

Why start by logging how many hours a day you sit?

Your buttocks carry your body weight and rub against your clothes the entire time you’re seated, so sitting time is friction time. To guess why the color darkened, you first need to know how many hours a day that adds up to.

The National Health Information Portal of the Korea Disease Control and Prevention Agency (KDCA) explains that when skin is pressed or rubbed, or when you sweat heavily, the skin’s defenses are damaged and boils form more easily. A student sitting in the library more than 10 hours a day before exams, an office worker in a desk chair all day, and someone who drives long distances all have different conditions. If you write down your total sitting time along with how many times you got up, you can match lifestyle changes to your photos later.

What should you note about your chair and clothes?

Two things are enough: whether you sweat against it, and how tight it is. Even over the same 8 hours, sitting on a chair that doesn’t breathe in tight pants stacks pressure on top of sweat.

For the chair, note whether it has a surface that doesn’t absorb sweat, like faux leather, and whether you use a cushion or cover. For clothes, note in that day’s column whether you wore close-fitting bottoms like jeans or leggings, or loose cotton. If you sat for a long time in wet clothes after a workout, log that time separately too. These items are an editorial rule that turns the pressure, friction and sweat the KDCA points to into everyday situations; the sources behind this guide include no study that directly compared chairs or clothing fabrics.

How hard are you scrubbing in the shower?

If you tend to scrub your buttocks hard with an exfoliating towel or a rough shower tool, that adds one more source of friction. Give your shower tool and pressure a column of their own in the log.

In a 2018 study, 6 healthy adults washed one forearm with a nylon towel and soap and the other with soap alone, twice a day for 2 weeks; on the towel-scrubbed side, skin water loss went up and natural moisturizing factor went down (grade B, small study on arms). It didn’t look at buttocks, but it does suggest that repeated scrubbing can weaken the outer layer of skin. Spread lather with your hands, and press water off with a towel instead of rubbing.

How do you keep track of dark marks left where bumps were?

Color left where a bump cleared often lasts a long time, so check only its direction with a photo taken under the same conditions once a month. In between, the key to the log is not picking or scratching new bumps.

In a 2016 study of 324 acne patients across seven Asian countries, 58.2% had dark marks after acne, and in half or more of them the marks lasted a year or longer, with 22.3% lasting 5 years or longer. The Korean Dermatological Association also explains that dark marks after acne can persist for a year or more. Some pigment comes from friction alone — enough that a 2012 study focused on 52 patients with frictional dermal melanosis. If a wide area darkened where there were never any bumps, give the friction side of your log more weight.

One-month daily-life log

Week	Average daily sitting time and times you stood up	Chair and bottoms (sweaty, tight)	Shower tool and scrubbing pressure	Days you picked or scratched	New bumps
Week 1
Week 2
Week 3
Week 4
End of month	One photo, same light and distance	Compare side by side with last month’s photo

Once you have three months of end-of-month photos, check whether the color got darker in months with long sitting hours and many picking days. If the color keeps spreading even after you changed your habits, the next step is taking your log to an appointment.

When is it time to bring it to a dermatologist?

• If a painful, firm lump forms where you sit or fills with pus, don’t squeeze it; get it checked. The KDCA warns that forcing it out before it comes to a head can make it worse.
• If red streaks spread out from the lump or nearby lymph nodes feel sore, get care right away.
• If three months of logging show the color getting darker and wider even after you changed your habits, have a dermatologist find the cause.
• If itching, oozing or scaly flakes come along with it, it may be a different skin condition, so consider an appointment.

What this guide is built on

• In a 2016 survey of 324 acne patients in seven Asian countries, 58.2% had dark marks after acne, and 22.3% lasted 5 years or longer.
• In a 2018 study of 6 healthy adults, the forearm scrubbed with a nylon towel twice a day for 2 weeks lost more water than the one washed with soap alone.
• A 2012 study of 52 patients with frictional dermal melanosis shows that friction can be one cause of pigment changes.