Fluid dynamics, 2019
APS/DFD 2019 in Seattle, looked back on
In November 2019 the 72nd annual meeting of the American Physical Society's Division of Fluid Dynamics took place at the Washington State Convention Center in Seattle. It is one of the largest conferences in fluid dynamics, with 3,000 or more attendees expected that year. These notes keep its subject: how fluids move.Independent page. This is not the American Physical Society, its Division of Fluid Dynamics or the 2019 meeting site.
Updated 2026-10-26
What a fluid dynamics meeting covers
- Turbulence and vortices: how smooth flow breaks into eddies, from pipes to the wake behind a cylinder.
- Flow made visible: dye, smoke and particles that show a flow, the theme of the Gallery of Fluid Motion.
- Short talks: results packed into a few minutes, see instructions for speakers.
- The host city: a cool, wet November, see Seattle weather.
From fluid dynamics to the fluids in your skin
Fluid dynamics covers every liquid that moves, including two that the human body pushes out through the skin: sweat and sebum. Sebum is the oil that keeps skin from drying out. It is made in a small gland beside each hair follicle and flows up that narrow opening to the surface. The NIH's skin disease institute (NIAMS) describes what happens when that flow stops: the follicle gets clogged, sebum and dead skin cells plug the pore, bacteria that normally live on the skin grow in the blocked follicle, and the result is the outbreak most people call pimples.
So the flow that matters on your face is plain: oil has to keep moving out of the pore. Each step below keeps that path open or treats it once it is blocked. Together they are the core of the how to get rid of pimples guide from howtogetridofpimples.org, which follows in full on this page.
- Keep the opening clear: wash gently twice a day and after sweating.
- Loosen the plug: adapalene or salicylic acid unclog pores.
- Calm the blocked follicle: benzoyl peroxide works on the bacteria.
- Leave it alone: NIAMS lists squeezing or picking among the things that make acne worse.
Source: NIAMS (National Institutes of Health), Acne overview
The full guide, reproduced from howtogetridofpimples.org
How to get rid of pimples, whiteheads, blackheads and acne cysts
How to get rid of pimples depends on the kind: adapalene for clogged pores, benzoyl peroxide for red bumps, a warm compress then a dermatologist for deep lumps. Per the AAD, one product needs 6 to 8 weeks.
Last reviewed · based on 5 dermatology sources
How to get rid of pimples, step by step
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Tonight
Wash gently
Wash your face up to twice a day and after sweating, using your fingertips and a gentle, non-abrasive cleanser. Scrubbing irritates the skin. After sports, wash as soon as you can.
Treat the whole area
Spread a thin layer of one product over all acne-prone skin, not just the spot: benzoyl peroxide, adapalene or salicylic acid. For adapalene, a pea-sized amount covers your whole face, every other night at first.
Cover it
Put a hydrocolloid pimple patch on an open pimple. Worn overnight, it can speed up healing and calm irritation.
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This week
Hands off
Don't pick, pop or squeeze. It makes acne take longer to clear and raises the risk of scars and dark spots.
Deep, painful pimple
Hold a clean, warm, damp washcloth on it for 10 to 15 minutes, three times a day, to bring it to the surface. Then use a thin layer of one acne product. If it won't go, a dermatologist can treat it, for example with a steroid injection.
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6-8 weeks
Be patient
Give one product 6 to 8 weeks. If it works, you should see some improvement in 4 to 6 weeks; clearing can take 2 to 3 months. No change after 6 to 8 weeks? See a dermatologist.
Once it clears, keep using it. Staying on it is how to get rid of pimples that keep coming back.
What to put on a pimple
An over-the-counter pimple treatment is an acne product you can buy without a prescription. It means you can start tonight with one active ingredient. The strength of each product is printed on the label; use it as often as the label says, since too much dries skin out.
| Ingredient | What it does | Best for | Strength | How long |
|---|---|---|---|---|
| Benzoyl peroxide | Kills acne-causing bacteria and reduces inflammation | Red, inflamed pimples | Washes and creams | 6 to 8 weeks |
| Salicylic acid | Removes dead skin cells, cuts oil, unclogs pores | Papules and pustules | Washes and leave-on products; follow the label | 6 to 8 weeks |
| Adapalene | A retinoid: unclogs pores and reduces oiliness | Blackheads and whiteheads | Gel without a prescription; stronger with one | A few months before trying stronger |
| Azelaic acid | One of four acne-fighting ingredients dermatologists name | A deep pimple once it surfaces | Sold without a prescription | 6 to 8 weeks |
Using more than one or two products at once can irritate your skin. For a single spot, an acne spot treatment dabbed only on that pimple keeps the rest of your face calm.
How to get rid of pimples by type
A pimple type is the kind of acne blemish you see, from a clogged pore to a deep cyst. It means each type needs a different treatment, so knowing yours tells you how to get rid of pimples of that kind. The depth of a pimple decides whether you can treat it at home. A sore lump that sits deep and never forms a head may be cystic acne, which is one for a dermatologist to see early.
- Whiteheads
- Closed, clogged pore. A pore clogged with oil, bacteria and dead skin cells that closed up: a tiny white or flesh-colored bump. Adapalene plus a benzoyl peroxide wash.
- Blackheads
- Open, clogged pore. A clogged pore that stays open. The dark dot isn't dirt, so don't scrub it. Adapalene plus a benzoyl peroxide wash.
- Papules
- Small, red, hard bump. Small, red bumps that feel hard. Lots of them can feel like sandpaper. Wash twice a day with benzoyl peroxide or salicylic acid.
- Pustules
- Red bump, white center. Like papules, but with a white or yellow center. Benzoyl peroxide or salicylic acid wash; don't pop.
- Nodules
- Deep, hard, painful lump. Deep under the skin. They often leave scars. A warm compress, then a dermatologist.
- Cysts
- Deep, filled sac. Deep, painful lumps you may feel more than see. They often scar. See a dermatologist early: fewer scars.
What to skip
- ScrubbingWashcloths, sponges and scrubs irritate acne-prone skin and make acne worse.
- PoppingIt slows healing and raises the risk of scars and dark spots.
- Toners and astringentsThey can dry your skin and make acne look worse. Look for "alcohol-free" on the label.
- Switching every few daysNew products too often irritate your skin and cause breakouts.
- TanningTanning damages skin and can worsen acne. Use a non-comedogenic SPF 30+ sunscreen.
When to see a dermatologist
A dermatologist is a doctor who treats skin, including acne that home care can't clear. It means you get prescription treatment, such as tretinoin, and procedures like chemical peels, light therapy or steroid injections. Go if you have:
- Painful lumps under the skin (nodules or cysts)
- Scarring
- No change after 6 to 8 weeks of products you bought yourself
- Acne that hurts your mood or confidence
Your questions, answered
Straight answers to what people search for most.
How do you get rid of a pimple overnight?
You can't make one disappear by tomorrow. Nothing works that fast. What helps tonight: a pimple patch on an open pimple, worn overnight, and keeping your hands off it.
For the full routine by type of spot, see our page on how to get rid of a pimple overnight.
Do pimples heal faster popped or unpopped?
Unpopped. Popping makes acne take longer to clear and raises your risk of scars and dark spots.
Do pimple patches really work?
On an open pimple, yes. The hydrocolloid in them absorbs fluid and forms a protective gel. Worn overnight, they can speed up healing and calm irritation.
What kills pimples best?
There's no single winner. Benzoyl peroxide kills acne-causing bacteria, adapalene unclogs pores, and salicylic acid unclogs pores and eases inflammation. The best one is the one that fits your pimple type.
What is the #1 cause of acne?
Clogged pores. Extra oil and dead skin cells block a pore, and bacteria grow in it. Hormones, genes and things around you play a part too.
Sources
- American Academy of Dermatology. 6 skin care habits that can clear acne.
- American Academy of Dermatology. Treating deep, painful pimples.
- American Academy of Dermatology. Acne: types of breakouts.
- American Academy of Dermatology. Acne: tips for clearer skin.
- MedlinePlus. Salicylic acid topical. medlineplus.gov/druginfo/meds/a607072.html
Last reviewed
This page is general information, not a diagnosis. See a dermatologist if you have painful lumps (nodules or cysts), scarring, no change after 6 to 8 weeks, or if acne affects your mood.