September 3, 2026 Kiran Nagra

Your Bloods Are Normal and Your Skin Isn't

You've had the bloods done. Testosterone: normal. DHEA: normal. Your cycle turns up more or less when it should, so you're clearly ovulating, and you've been told — reasonably, kindly, and with the results right there on the screen — that your hormones are fine.

And yet. You break out around ovulation. You break out the week before your period. Some months your skin is clear enough that you think you've finally cracked it, and then the next month it's back along the jaw and the chin, and nothing you did differently accounts for either.

Here's what nobody explains: the amount of testosterone in your blood was never the thing that determines what your skin does. It's one input into a system with at least three amplifiers and two brakes, and every single one of them varies — across your cycle, and from one month to the next. Your blood test measured one number, once. It didn't measure the system.

So let's go through the system properly, because once you can see it, the pattern that's been baffling you turns out to be extremely orderly.

Between your blood test and your skin, there are three amplifiers

Testosterone in your bloodstream isn't what acts on an oil gland. It's raw material, and it goes through three multiplication steps on the way in. None of them appear on a standard panel.

Amplifier one: how much of it is actually free. Most of your testosterone is bound to a carrier protein called SHBG (sex hormone binding globulin), and while it's bound, it's inert — like money locked in a term deposit. Only the free fraction can act on tissue. Here's why that matters enormously: insulin suppresses SHBG. A stretch of poor sleep, more refined carbohydrate than usual, a stressful few weeks with the blood sugar all over the place — SHBG drops, and your free testosterone climbs even though your total testosterone hasn't moved a millimetre. Two women with identical total testosterone can have completely different free testosterone. And standard panels usually report total.

Amplifier two: how much gets converted. Once testosterone reaches the skin, an enzyme called 5-alpha-reductase converts it into DHT — dihydrotestosterone — right there inside the oil gland and hair follicle. DHT is roughly three times more potent than the testosterone it came from, and by some measures of receptor binding considerably more. How fast you run that conversion varies hugely between women and you cannot infer it from the precursor level.

Amplifier three: how loudly the receptor hears it. The androgen receptor itself comes in more and less sensitive versions, determined by a repeating sequence in the gene — and shorter sequences make a more responsive receptor. This has been measured directly: women with acne averaged around 20 repeats, women with hirsutism around 16, against roughly 21 in women with neither. Fewer repeats, louder signal, same hormone. This is the real answer to why me and why not her — and it's not something you can change, though it's worth knowing, because it tells you your skin was always going to respond to what everyone else's skin ignores.

Stack those three together and a perfectly normal testosterone result can be arriving at your oil gland as a signal several times over. Your blood test shows how much fuel is in the tank. It says nothing about the fuel line, the injectors, or how sensitive the engine is.

It was never about how much testosterone. It's about what's opposing it.

Now the part that actually explains your cycle.

Testosterone barely moves across the month. It's remarkably steady, with a modest bump around ovulation and otherwise a fairly flat line. If testosterone were driving your breakouts, they'd be constant.

What swings enormously is everything opposing it. Estrogen and progesterone rise and crash across every cycle, and both of them restrain androgen activity in your skin — by completely different routes.

Estrogen brakes in two places at once. At the oil gland it directly restrains sebum production and keeps the surface layer of skin thick and hydrated. And in the liver it raises SHBG — which means more of your testosterone gets locked into the term deposit and less of it is free to act. So when estrogen falls, you don't get one problem. You get two simultaneously: the brake comes off at the gland, and your free testosterone rises. Same total testosterone on paper. More of it available, and less opposing it.

Progesterone brakes somewhere else entirely, and this is the one almost nobody knows about. Come back to it in a moment, because it's the answer to your month-to-month question.

So here's the reframe that changes how you read your own skin: nothing goes up before a breakout. Something goes down. Your androgens have been sitting at the same level all along. The tide goes out, and the rocks that were always there are suddenly above the water.

Why you break out at ovulation and the week before your period

These look like the same problem happening twice. They're two different ratio events with two different mechanisms, which is why they can feel slightly different and why some women only get one of them.

At ovulation: estrogen climbs to its highest point of the month, triggers the LH surge, and then drops sharply immediately afterwards — before progesterone has risen enough to take over. There's a short window mid-cycle where estrogen has fallen off its peak and progesterone hasn't arrived yet. On top of that, the LH surge itself stimulates the theca cells in your ovary, which produce androgens — so you get a small androgen bump at precisely the moment your estrogen brake is briefly off. Estrogen dip and androgen bump, overlapping, for a couple of days. That's your ovulation breakout, and it usually shows up 3–5 days later once the follicle has had time to clog and inflame.

The week before your period: estrogen and progesterone both fall away as the corpus luteum winds down, but estrogen falls proportionally harder and faster. Testosterone doesn't rise — it simply ends up sitting above both of them. This is the classic jaw-and-chin premenstrual flare, and the margin involved is small. Whether your testosterone finishes that week a fraction above the line or a fraction below it is the difference between a clear month and a wrecked one.

Why it's clear one month and a disaster the next

This is the question I get asked most, and the answer is one of the most satisfying pieces of biochemistry in women's health.

The variable isn't your testosterone. It's your progesterone — and specifically, whether you ovulated well that particular month.

Start with something that surprises most women: a regular period is not proof of a good ovulation. You can bleed on time, every 28 days, on a cycle where the follicle released late or the corpus luteum that formed afterwards was weak and short-lived and produced very little progesterone. From the outside, that month looked identical. Inside, it wasn't.

And here's why that lands on your face. Progesterone is a substrate for 5-alpha-reductase — the exact same enzyme that converts testosterone into DHT. Both molecules queue for the same enzyme. When progesterone is abundant, it occupies enzyme capacity and competitively inhibits the conversion; in laboratory work on skin tissue, progesterone inhibits 5-alpha-reductase activity by as much as 97% at high concentrations. And in women who sustain a proper progesterone rise through the second half of their cycle, DHT has been observed to actually fall slightly in the late luteal phase.

So run the two months side by side.

Month one: you ovulated strongly, built a robust corpus luteum, made good progesterone. That progesterone occupies the enzyme. Less of your testosterone gets converted to DHT. Your skin is calm, and you assume the new routine is working.

Month two: you were run down, slept badly, trained hard, ate erratically, had a rough fortnight at work. Ovulation was weaker and progesterone was low. The enzyme is now free. The identical amount of testosterone converts far harder into DHT — and you break out, and you cannot work out what you did differently.

You didn't do anything differently with your androgens. You lost the brake. And a blood test taken in either month would have said your testosterone was normal, because in both months it was.

This is also where cortisol enters properly — not as vague "stress affects skin" advice, but as a specific link in this chain. Sustained stress suppresses the hypothalamic signalling that drives a clean LH surge, which produces exactly the weak ovulation and poor luteal progesterone described above. A stressful month is a low-progesterone month is a high-conversion month. Cortisol also appears to change what your sebum is made of, shifting it thicker and stickier so it clogs a pore more readily — that part is a working model rather than settled fact, but it's the difference between water and honey going down the same drain. Same amount, different result.

One more thing worth knowing, because it matters clinically: this braking effect belongs to progesterone specifically. Medroxyprogesterone acetate, a synthetic progestin, does not inhibit 5-alpha-reductase in the same way. The molecule matters, not just the category.

Where a hormonal IUD fits — and why nobody connects it

Which brings us to a pattern I see constantly and which almost never gets joined up.

Some progestins used in devices and contraception are derived from a testosterone-like backbone and carry mild androgenic activity of their own. So you get a steady androgenic input — without the 5-alpha-reductase braking that your own progesterone would have provided. In a woman whose testosterone already sits at the upper end of normal, that combination produces year-round what the premenstrual week used to produce for a few days.

The reason it slips past everybody is the delay. A device fitted eight months ago and skin that changed six months ago don't feel related, so they never end up in the same sentence. To be very clear: plenty of women use hormonal IUDs with no effect on their skin at all, and this isn't an argument against them. It's an argument for the question being asked, because usually nobody asks it.

The hair vitamin that may be feeding it

Worth checking before you go any further, because it's sitting in a lot of kitchen cabinets.

Vitamin B12 and biotin — the two headline ingredients in nearly every hair, skin and nails supplement — can make acne worse.

The B12 mechanism is a beautiful one, because B12 doesn't act on your skin at all. It acts on the bacteria living in your pores. Cutibacterium acnes normally manufactures its own B12. Flood it with supplemental B12 and it shuts down that production and reroutes its metabolism — and one product of that rerouting is porphyrins, which are directly inflammatory inside the follicle. Same organism, different behaviour, more inflammation. In the original work, one in ten supplemented subjects developed acne within a week.

The supplement you bought for your skin is having a conversation with something else that lives in it.

Biotin's link to acne is weaker — the usual explanation is competition with pantothenic acid, and the evidence is largely observational — but it travels in the same bottle. Separately and importantly: biotin interferes with a number of common blood tests, thyroid panels especially, and can distort the results badly enough to produce a misleading picture. If you're taking it, say so before you're tested.

And the reason none of this surfaces is that a hair supplement doesn't feel like a medication. It lives with the supplements, not the prescriptions, so it never makes it onto the list when someone asks what you're taking.

What to actually ask now

The question that produced your normal result was are my androgens high? It's a reasonable question and you have your answer. It's just the wrong one.

The better ones:

How much of my testosterone is free, not total? Free is what acts. Total is what usually gets reported.
How much am I converting into DHT? A comprehensive urine hormone panel — DUTCH is the one most people have heard of — reports the metabolites your body actually made, including a marker reflecting how much DHT was generated inside your tissue. That's the conversion step, made visible. It doesn't diagnose anything on its own and it doesn't treat anything. It answers the question blood was never built to answer.
Am I ovulating well, not just bleeding regularly? Given everything above, this is arguably the most important question on the list, and it's the one least often asked.
What else has quietly joined the picture? A device, a hair supplement, a long run of insufficient sleep, a period of relentless pressure — any of which acts on this system without ever looking like a skin problem.

You're not imagining it and your test wasn't wrong. Your androgens really are normal. It's what's happening to them after the blood draw — how much is free, how hard it's converting, how sensitively you receive it, and how much brake you built that month — that your skin has been reporting all along.