Shiny, not dewy: how to keep oily skin calm in a heatwave

A cosmetic chemist on why heat makes oily skin worse, the science-backed routine that calms it, the summer breakouts that aren't even acne and why 10%-20% niacinamide might work better for oily skin.

Jul 11, 2026

With summer keeping hot, I really do feel for you, my oily-skin Complexions, because I expect quite a few of you are noticing your skin looking shinier day by day, and not the good kind of gloss or dewiness we chase. This kind of gloss can bring breakouts, clogging, and fungal acne along with it.

So let's talk about keeping oily skin under control during summer, and what a science-backed routine actually looks like for skin like ours. But this time I'm going further than the routine: supplements, lifestyle, and first-hand experience as an oily, acne-prone gal who has finally cracked staying (mostly) clear through the hot months.

The protocol (save this)

Morning

Gentle, low-pH gel or foaming cleanser (aim for under ~5.5; there’s a whole section on why below). If you wake up not-that-oily, plain water is fine. You’re not “dirty” in the morning.
Optional: a niacinamide serum (2-10%, more on the high end later), or a niacinamide + zinc PCA combo.
A lightweight humectant if you need it: glycerin or hyaluronic acid, gel texture.
Broad-spectrum SPF 30-50, fluid or gel-cream, matte finish. Reapply every couple of hours if you’re out in it. This is the step that ACTUALLY matters.

Evening

Cleanse. Double cleanse only if you’ve worn heavy SPF or sweated buckets: an oil-free micellar or gel first, then your normal cleanser. You do not need to strip your face.
One active, rotated, not all at once:
- Oily/congested → salicylic acid (0.5-2% leave-on) or azelaic acid (15-20%).
- Inflammatory spots → adapalene 0.1%, starting a couple of nights a week.
- Itchy, uniform little bumps on chest/back/hairline that won’t respond to acne stuff → think fungal, not bacterial (I’ll explain).
Lightweight moisturiser or a ceramide gel-cream to keep the barrier happy.

The non-negotiables

Cool the skin down where you can. Temperature is doing more than you think.
Don’t over-cleanse. Stripped skin makes more oil, not less.
Use a low-pH cleanser (under ~5.5). The acid mantle matters more for us than most people realise (section below).

Supplements worth considering (adjuncts, never substitutes): zinc, omega-3, and vitamin D if you’re deficient. Everything else is optional at best.

Right. Now the why.

Why your skin turns up the oil in July

This isn’t in your head. Heat literally increases oil.

The classic figure comes from Cunliffe and colleagues back in 1970: sebum excretion changes by roughly 10% for every 1°C change in skin surface temperature. Warm the skin, oil goes up; cool it, oil comes down. It’s a small study and the authors were careful to say they were measuring sebum reaching the surface, which is partly about the oil getting runnier and spreading, not purely about the gland making more. I like that nuance, because it also hints at why simply cooling your face feels like it works.

We’re no longer relying on a 1970 paper, though. A 2025 randomised crossover trial sat thirty people at 22°C and then at 32°C for two hours each. At the warmer temperature, sebum secretion rose significantly, skin glossiness jumped by about a third, and inflammatory markers (IL-1α) went up too. So heat doesn’t just make you shinier: it pushes the skin towards a more inflamed state. That’s the part that turns “shiny” into “spotty.”

Quickly on the mechanism. Our skin carries temperature-sensing TRP channels, and the warmth-tuned ones flip on right around the temperature of a hot day. However, that evidence is mostly lab-dish and it’s messy (in some experiments switching one of these channels on actually lowers oil), so it isn’t a tidy story. However, it’s useful for understanding. Treat it as “there’s a mechanism there somewhere,” not gospel.

And your skin’s microbiome shifts with the seasons too, so the mix of microbes on our faces isn’t the same in August as it is in January. And this is where some summer “acne” advice I see online goes wrong.

Is it even acne? (Often, no.)

I’ve been with you, guiding you through skincare on social media for over six years now, and from speaking to some of you, I feel I can say that a lot of you feel like nothing works in summer, and that’s because what you’re treating is the wrong thing entirely.

Fungal folliculitis (Malassezia folliculitis, the thing the internet insists on calling “fungal acne”) is an overgrowth of a yeast that lives on all of us and adores heat, humidity, sweat and occlusion. It shows up as small, itchy, uniform bumps (they all look the same, and there are no blackheads or whiteheads), usually across the chest, back, forehead, cheeks, shoulders and hairline. It likes oily areas, since the yeast feeds on sebum.

It’s frequently misdiagnosed and treated as ordinary acne first, for years. And here’s the cruel twist: antibiotics, a mainstay of bacterial acne, can make it worse by clearing out the competition. It responds to antifungals: an anti-dandruff wash with ketoconazole, zinc pyrithione, or selenium sulphide left on for a few minutes, and in stubborn cases oral itraconazole, which clears the great majority of cases where acne treatment had failed.

If your “acne” is itchy, samey and stuck on the areas I’ve mentioned above, please try treating it as fungal before you escalate your acne routine.

Acne aestivalis, or “Mallorca acne”, is different again: monomorphic, comedone-free little bumps that appear a day or two after sun exposure, driven by UV rather than bacteria. It’s really a cousin of a sun allergy. Antibacterial acne treatment won’t touch it; sun protection is the actual answer.

And miliaria (heat rash) is simply blocked sweat ducts: cool down, dry off, stop occluding, and it settles.

Piling on a stronger acne serum won’t fix any of these. Working out which one you’ve actually got will.

My Chemist-Vetted antifungal / fungal-folliculitis picks: [LINK]

The stuff that works.

Salicylic acid is my summer hero. It’s oil-soluble, so it gets down into the pore where the congestion is, it’s genuinely comedolytic, and it’s mildly anti-inflammatory on top. I call it “the plastificator”, because it works its way into that thick, sticky sebum and loosens the plug so it stops getting jammed in the pore. A 0.5-2% leave-on does the job for most people. It suits sweaty, congested, hot-weather skin better than almost anything.

My Chemist-Vetted salicylic acid picks: [LINK]

Azelaic acid is the quiet all-rounder I think everyone with summer congestion should know. It’s antibacterial, anti-inflammatory, helps with texture, and it inhibits the enzyme behind pigment, which matters enormously in summer when every spot threatens to leave a brown mark. At 15-20% it held its own against adapalene in trials, with less irritation. Those higher strengths are prescription-only here in the UK, but don’t write off the lower-concentration OTC versions (around 10% some higher though still not equal to prescription ), they still do plenty of good; they’re just gentler and slower to show results than the prescription stuff, which can actually be a plus if your skin irritates easily. If you only add one new thing, this is a strong pick.

My Chemist-Vetted azelaic acid picks: [LINK]

Adapalene (0.1%) is the retinoid I’d reach for in the heat, mostly because it’s gentler on sensitive skin and photostable in a way other retinoids aren’t. Still wear your SPF, still start slow (two or three nights a week and build), because a stinging, stripped barrier in a heatwave helps nobody.

And if you’re a long-time follower, I don’t think I need to remind you to pair it with ectoine (3-7%) for better tolerance. If you’re new here and haven’t met this pro tip yet, here it is: buffering your retinoid with ectoine has saved just about everyone who’s listened to me online, myself included, from a world of irritation and a damaged skin barrier.

My Chemist-Vetted ectoine products to pair with retinoids: [LINK]

Niacinamide + zinc PCA is the gentle daily backbone. Niacinamide is anti-inflammatory and barrier-supporting with a real (if modest) oil-reducing signal; zinc PCA brings a mild oil-regulating, anti-microbial hand, and the PCA part is a humectant. Lovely and light for hot weather. Just know it’s a low-drama supporter, not a miracle.

My Chemist-Vetted niacinamide picks: [LINK] ( opt for light serum, rathen an emulsion )

Now, this is what some of you have been asking about.

Does high-dose niacinamide (10%, even 20%) really “normalise” oil?

I spent a good while looking at and analysing the evidence on this one, putting the pieces together, and this is where that master’s in biochemistry really came in handy. So here’s my conclusion. For now, at least.

The proper sebum studies were done at 2-5%. There is no independent controlled trial showing 10% or 20% does more for oil. The high-dose claim is clinical observation and anecdote. And I bet most people don’t realise that even at the studied doses, the mechanism behind niacinamide’s oil-lowering effect is officially unknown. So we’re theorising about a dose-response for an effect nobody has fully explained. So keep that in mind while I walk through why a well-made high dose might still do something extra.

The boring, most likely reason: it's about delivery. Niacinamide is tiny and very water-loving, and the oil gland sits deep in the follicle in a fatty environment that water-loving molecules reach badly. How much gets across the skin scales with the concentration gradient, so 20% pushes far more molecule towards the gland than 2%. Low doses might be doing their thing at the surface while never really reaching the target, and the high-dose "sweet spot" is just pharmacokinetics. This is also where "formulated well" does the heavy lifting: the right vehicle and avoiding the gritty crystallisation you get shoving niacinamide to 20% decide whether that extra concentration reaches the gland or just sits there feeling tacky.

Now a more speculative one: a bit of it might turn into niacin. There'll be a bit of biochem jargon in this part, but please bear with me. Niacinamide (the amide) and niacin (nicotinic acid) are not the same at the receptor (the lock a molecule slots into). Niacin switches on a receptor called HCA2 on our oil cells, which triggers a calcium signal (a message passed inside the cell) that calms oil production; silence the receptor and the effect vanishes. Niacinamide barely touches HCA2 on its own. But the amide can slowly convert to nicotinic acid, a reaction that heat, time and low pH all encourage, and at a 20% starting point, even a tiny percentage converting gives you a meaningful amount of niacin right where you want it. So high-dose niacinamide might partly be acting as a slow-release niacin depot, sneaking in through a door the amide can't open itself. The giveaway would be a flush or tingle, because that same HCA2 activation is what makes niacin flush, which is precisely why a clean, pH-controlled high dose behaves so differently from a badly made one. There's a lovely irony there: the impurity that causes the sting might be part of the effect.

The reason that best fits the word “normalise” is your barrier. A stripped, over-washed barrier drives compensatory oil: the skin panics and overproduces. Niacinamide reinforces the barrier (it boosts ceramide production), and a higher dose plausibly does that more robustly. So some of what reads as “oil control” might really be breaking the over-cleanse-then-overproduce cycle. Which sounds a lot more like “normalising” than just switching the gland off.

To conclude, if high-dose works, it’s most likely down to delivery, possibly with a little niacin conversion on top. And the barrier support is probably what makes it feel like it’s normalising your oil rather than just switching it off. It’d be great if someone did some proper testing on high-dose niacinamide, but that’s probably wishful thinking. Something I noticed in my battle with summer oily skin, a well formulated 10%-20% niacinamide serum keeps my skin very happy and less oily.

Sulphur is the “dark horse” of this list. It’s underrated, barely mentioned, and ties straight back to that fungal conversation: it’s keratolytic, antibacterial and antifungal, which makes it quietly brilliant for these fungal flare-ups. It’s old-fashioned and it smells, so I treat it as a targeted spot or wash-off rather than an all-over daily.

My Chemist-Vetted sulphur picks: [LINK]

Benzoyl peroxide. It works, and it's worth spending a few moments and clearing up the benzene scare you might have seen. In 2024 an independent lab reported that BPO can degrade into benzene, a carcinogen, but most of those alarming figures came from baking the products at 50 to 70°C, temperatures you're told to keep them well away from anyway, and the method drew a lot of criticism. When the FDA ran its own testing, over 90% of products had undetectable or very low benzene, only a handful of specific lots were recalled, and consumers weren't told to stop using anything. So it's not the emergency it was billed as. If you want the full teardown, Dr Michelle Wong at Lab Muffin did a whole series picking the data apart and even co-authored a peer-reviewed paper on it, she's who I'd send you to on this. Heat and light still aren't kind to BPO, so keeping it somewhere cool rather than letting it cook in a hot car is sensible enough, but you don't need to refrigerate it or bin it every month. (It also bleaches every towel and pillowcase you own, which in sweaty season is its own small tragedy.)

Sunscreen I’ll die on this hill!! This is THE MOST important step, full stop, for pigment, for photoageing, and for keeping Mallorca acne away.

I don’t want to hear that sunscreen clogs your pores. There are sunscreens for literally every skin type now. And I have news for you, UV is clogging your pores even more, as it turns certain components of your sebum into highly comedogenic molecules that no amount of shea butter can compare to.

Know someone who skips SPF because it "clogs their pores"? Send them this one.

The trick for oily skin is texture. A fluid, gel-cream or “dry-touch” matte finish gets worn and reapplied, and the sunscreen you reapply is the one that works. Mineral filters like zinc oxide suit reactive skin and read more matte (the trade-off is a possible cast). Top up every couple of hours in real sun. Elegance here isn’t vanity. It’s adherence.

For a properly matte, velvety finish, look for silica on the label, it’s a fine powder that mops up shine and blurs the surface. And on high denatured alcohol (alcohol denat, often sitting near the top of lightweight fluid sunscreens): it’s fine for most people, and it’s exactly what gives those featherlight textures their fast-drying feel, so it isn’t something to fear. But at high levels it can be drying enough, in some people, to nudge that barrier-then-overproduce loop from earlier, and the skin ends up feeling oilier over time. It’s individual, not universal. Keep half an eye on it: if your skin started looking and feeling a lot oilier once you switched to a high-alcohol formula, you’re not imagining it, and it’s worth trying one without.

My Chemist-Vetted oily-skin SPF picks: [LINK]

Texture, and the words on the label

The whole philosophy in heat is lighter, not more. Gels, gel-creams, fluids, light lotions. Thin layers of hydration, I call it. Heavy balms and rich oils trap heat and sweat and feed exactly the occlusion problems (miliaria, folliculitis) we’re trying to avoid.

And I have to say this: “oil-free” and “non-comedogenic” are barely regulated and only loosely meaningful. There’s no agreed test; the old rabbit-ear assay everyone quotes over-calls things badly, as its own creators later admitted. Whether something clogs you depends on the finished formula in real use, not on scanning an ingredient list for villains. Trust in-use human testing and your own skin more.

My Chemist-Vetted oily-skin moisturisers picks: [LINK]

Last thing on cleansing: please don’t over-do it. Squeaky-clean is a barrier injury, and a stripped barrier answers by making more oil. Twice a day, gently, plus a rinse after heavy sweat, is plenty.

A word on low-pH cleansers

I’ve seen a couple of creators post about switching to low-pH cleansers, after noticing that cleansers around pH 6 to 6.5 left their acne-prone skin feeling tight and looking worse. And that’s not without grounds. Healthy skin sits behind a slightly acidic film, the acid mantle, with a surface pH averaging around 4.7, generally in the 4.5 to 5.5 range. That acidity isn’t trivia; it’s functional. The enzymes that build and repair your barrier work best in that acidic window, the enzymes that break the barrier down are held in check by it, your friendly flora cling on better when it’s acidic, and (the part that matters for breakouts) C. acnes gets more comfortable as the surface drifts up towards neutral.

Skin like ours tends to sit at the higher, less-acidic end of that range. Acne-prone skin makes more sebum but, paradoxically, less free fatty acid, and free fatty acids are a big part of what acidifies the surface in the first place. So more oil doesn’t buy you more acidity; if anything, the reverse. This is a plausible mechanism, not a hard rule. So oily, acne-prone skin is usually less acidic than ideal.

Why care? A surface that’s crept toward neutral is a friendlier home for C. acnes, a slightly weaker barrier, and (through those pH-sensitive barrier-degrading enzymes) a nudge toward both barrier breakdown and the abnormal follicular shedding that sits behind comedones. It’s a small shift but real enough for downstream consequences.

The practical part is easy, just swap to a more acidic cleanser. Acidic (”syndet”) cleansers lower both skin-surface pH and propionibacterial counts compared with more neutral ones. So if your cleanser states its pH, keep it under about 5.5 (under 6 at the very most). Your leave-on acids help too (salicylic and azelaic, mostly prescription, are inherently low-pH), and a mildly acidic moisturiser nudges things the right way rather than fighting it. No need for pH strips or an obsession, just lean acidic where you can.

My Chemist-Vetted low-pH cleanser and acidic moisturiser picks: [LINK]

Lifestyle, the unglamorous stuff that actually moves the needle.

Cooling your skin lowers oil directly (that 10%-per-degree thing cuts both ways), so a cool flannel, a cooler bedroom, a refreshing facial mist during the day, ducking into the shade: all legitimately useful, not just nice.

The mist deserves a closer look, because it’s the one product that truly cools rather than just feeling like it does. No skincare ingredient lowers your skin’s temperature, the “cooling” actives just fool your cold receptors while the skin stays exactly as warm. What genuinely drops it is physics: as the water evaporates it lifts a little heat off your skin, the same way sweat does. The effect is short, a minute or so, but across a hot day it’s a real reset, and you can spritz it straight over SPF and makeup as long as you let it air-dry instead of rubbing. Keep the bottle in the fridge so you get cold water and evaporation together, and let it dry on its own rather than wiping it off, the drying is the cooling. If you’d rather it leave a little hydration behind instead of just evaporating away, choose a mist with a humectant like glycerin, or follow it with your lightweight gel. Then top up whenever the heat and shine start creeping back.

My favourite facial mists: [LINK]

Get sweat off promptly, and blot rather than rub. Sweat plus friction plus occlusion is the recipe for both heat rash and those breakouts along your hairline and jaw. Which is acne mechanica (pressure and friction acne), and the summer culprits are your phone held to your face, sunglasses, headbands, caps, straps, and masks. So wear breathable fabrics, keep your gear clean, and get your phone off your face.

On diet, the strongest signal by far is that high-glycaemic-load eating (lots of fast sugar) modestly worsens acne, and low-GL patterns modestly help. Dairy is mixed: a large meta-analysis found a small association, while more recent pooled work finds none. So it’s real but small, different for everyone, and worth testing on yourself rather than cutting things out in a panic. Diet plays a supporting role here, not a starring one.

By the way, obviously drinking enough water is good for you, but it won’t de-grease your face. The systematic review on water intake and skin hydration is thin and weak, with a slight benefit mainly in people who were barely drinking anything. Stay hydrated because it’s good for you. Don’t expect it to fix your T-zone.

A word on supplements

None of these replace a good routine or a doctor, they’re extras at best. With that said:

Zinc has the best evidence of the bunch: people with acne tend to run lower on it, and supplementing has reduced inflammatory spots in trials. But it’s also the one most likely to upset your stomach, and taking too much long-term can knock out your copper, so mind the upper limit and don’t megadose forever.

Omega-3 has a few small, promising trials for inflammatory lesions and a mixed picture for acne overall, but I’d take it anyway. It supports the skin barrier and comes with wider benefits for inflammation, heart health and healthy ageing, so it earns its place regardless of what it does for your spots.

Vitamin D is worth correcting if you’re deficient (a lot of us are), but chasing high levels isn’t the move, and it’s toxic in excess.

Probiotics show modest effects with low-to-moderate certainty: worth a try, not a promise.

And to be crystal clear because I care about you: high-dose vitamin A is NOT a supplement to self-prescribe. The real retinoid medicine (isotretinoin) is prescription-only and monitored for good reason. Please don’t go near mega-dose vitamin A on the internet’s say-so.

What I actually do

Since I promised first-hand: I do like an extensive routine for the anti-ageing benefits, but the minute I notice my skin getting oilier and duller in the heat, it all gets pared back, and that’s the point.

Mornings: water to refresh, then a watery NMF toner or mist (at least three layers), a salicylic acid toner (2-3 times a week), vitamin C (which I keep in for the anti-ageing side), niacinamide (I use 10 or 20%, but a well-formulated one), a light gel-cream hydrator, and a fluid SPF I don’t hate. Every single morning, reapplied.

At night, a few layers of toner again, then azelaic acid, then tretinoin 3-4 times a week (I’m well adjusted to tret, I used it daily for over a year and have since dropped the dose to maintain the results), though I’ll switch to adapalene if my skin gets too sensitive. And if I’ve got an inflamed spot, I keep the face on its usual schedule but dab tret straight onto that spot every night until it settles, just the spot, not all over. A lightweight barrier moisturiser to finish.

I cool my face down through the day with a mist. I stopped over-washing years ago and my oil is calmer for it. Consistency, light textures, and the right ingredients, that’s the whole thing.

Stay cool out there, Complexions. Your skin isn’t misbehaving; it’s just hot. Treat the right problem, keep it light, and let the barrier do its job.

M x

This is educational content from a cosmetic chemist and biochemist, not individual medical advice. Prescription-strength options and persistent or scarring acne warrant a dermatologist.