Does skincare get into your bloodstream when you're pregnant?

Some skincare ingredients do pass through your skin and into your bloodstream, and researchers have measured how much.

The amount varies enormously from one molecule to the next, which is why a short list of ingredients is worth avoiding in pregnancy and the rest are not.

This is the question sitting under every list of skincare ingredients to avoid during pregnancy you've read, so let's dive right in!

Yes, skincare ingredients can reach your bloodstream

Several topical ingredients are measurably absorbed into the bloodstream, and the figures are published.

When researchers applied a 2% hydroquinone cream to human volunteers for 24 hours, just over 45% of the dose was absorbed, and it showed up in blood samples taken at the first measurement, 30 minutes in.¹

A United States Food and Drug Administration randomised trial found the same thing with sunscreen filters.

Six filters went onto 48 healthy adults, and all 6 passed into the bloodstream above the regulator's 0.5 nanograms per millilitre threshold.

That was day one, after a single application. Oxybenzone from a lotion peaked at 258 nanograms per millilitre.²

So skincare does not always stay on the skin's surface. The useful question is which ingredients cross, and how much?

Why the amount varies so much from one ingredient to the next

How much of an ingredient reaches your bloodstream depends mostly on the molecule itself. For example, a serum and a moisturiser differ because the two molecules are not the same size or shape.

This matters more than any label claim. Two products can both be described as pregnancy safe and still behave completely differently once they are on your skin, because of what's inside them.

Five things drive the amount:

1. The size of the molecule
2. Its structure
3. The concentration used
4. The base it's formulated into
5. How long it stays on your skin before it is rinsed away.

What is the 500 Dalton rule?

The 500 Dalton rule is the observation that molecules bigger than about 500 Daltons struggle to get through the outer layer of skin at all.

A Dalton is simply a unit for the size of a molecule, in the same way grams are a unit for weight.

Two dermatologists set this out after reviewing which compounds reliably penetrate skin and which do not.

Almost every substance that works through intact skin, including the ones used as medicines, sits under 500 Daltons.³

Hydroquinone is 110 Daltons. Salicylic acid is 138. Niacinamide is 122. All three are small enough to pass.

Sodium hyaluronate, by contrast, runs into the tens of thousands of Daltons, and the vitamin C form used in our morning serum is about 1,130.

Why does hydroquinone absorb so much more than other skincare ingredients?

Hydroquinone absorbs more than almost any other skincare ingredient because it's a very small molecule, used at a relatively high strength, over large areas of skin and left on.

At 110 Daltons it moves through the outer layer easily. The human study above found just over 45% of a 2% cream dose absorbed in 24 hours, with most of it cleared through urine in the first day.¹

A review in Canadian Family Physician concluded that, apart from hydroquinone and tretinoin, skincare products for benign skin conditions act locally and produce minimal systemic levels.⁴

MotherSafe, run out of the Royal Hospital for Women in Sydney, advises avoiding hydroquinone in pregnancy for the same reason: it absorbs through skin in larger amounts than other products.⁵

What else changes how much gets through?

Beyond the molecule, four practical things change the amount:

1. Strength
2. The base it sits in
3. Time on skin and;
4. How much skin you cover.

The sunscreen trial shows the base clearly. The same filter, avobenzone, reached 7.1 nanograms per millilitre from a lotion and 3.3 from a pump spray.²

Same ingredient, different formula, roughly double the exposure.

Scale matters just as much. In that trial, sunscreen went onto 75% of body surface area, four times a day, for four days.²

A serum on your face is a tiny fraction of that, applied once or twice.

The amount of time a product sits on your skin is important too. A cleanser sits on your face for under a minute before it is rinsed off, so very little gets the chance to cross.

A review of topical products in pregnancy made the same point about salicylic acid: the risk is low when use stays on small areas and the caution is for high strengths e.g. in peels or use under a dressing.⁶

Do products that gets absorbed into your skin reach your baby?

What reaches your bloodstream can reach your baby, and that is exactly why the amount matters rather than the fact of absorption.

Where skin absorption is known to be minimal, the exposure to the baby is generally insignificant.⁵ 

Retinoids are the clearest example of what to avoid.

Topical tretinoin absorbs at around 4.5% of the applied dose.⁷ While this may seem low, any unnecessary fetal exposure to a known teratogen should be avoided. 

A review pooling 654 pregnancies exposed to topical retinoids in the first trimester found no significant increase in major congenital malformations.⁸ However, researchers explicitly warned that the study's sample size was too small to definitively prove safety.⁸

Because data cannot rule out severe risks, dermatologists universally advise against using retinoids during pregnancy.

How the molecules in a pregnancy routine compare

Once you know absorption tracks the molecule, choosing a formula becomes a question about the ingredients used. 

This is the lens we formulate through, and it's set out in full in our ingredient list.

Vitamin C is the clearest example. Pure ascorbic acid is 176 Daltons, small enough to pass through skin readily.

We chose tetrahexyldecyl ascorbate (THDA) instead, at roughly 1,130 Daltons, more than twice the 500 Dalton threshold, because it's also far more stable in a formula and less irritating on reactive pregnancy skin. THDA has improved ability to penetrate the epidermis due to its lipid structure.

Sodium hyaluronate goes further again, into the tens of thousands of Daltons, which puts it out of reach of the outer layer of skin entirely.

Here is how the molecules compare:

Does hyaluronic acid get into your bloodstream?

Hyaluronic acid does not reach your bloodstream in any meaningful amount, because the molecule is far too large to cross the outer layer of skin.

Researchers used a light-based imaging technique to track three sizes of hyaluronic acid through human skin.

The large versions, 1,000 to 1,400 kilodaltons, did not pass the outer layer at all. The smaller ones, 20 to 300 kilodaltons, did move through it.⁹

Keep the scale in mind. Even the small versions are 20,000 Daltons and up, which is 40 times the size at which molecules start to struggle.

Moving into the outer layer is also not the same as moving into blood.

A 2022 review of topical products in pregnancy describes hyaluronic acid as safe to use liberally.⁶ That matches what we see in practice, and is why it appears in several of our formulas.

There is more detail in our guide to hyaluronic acid during pregnancy.

Does niacinamide get into your bloodstream?

Niacinamide is small enough to pass through skin, so small amounts do reach your bloodstream. However it's not a safety problem. 

Niacinamide is the amide form of vitamin B3.¹⁰ It is a nutrient your body already runs on, and it is included in most pregnancy multivitamins at doses far higher than a serum could ever deliver through skin.

The question becomes not only about whether something crosses, it is what the molecule does once it is in.

Vitamin B3 crossing is unremarkable. Hydroquinone crossing is a problem, because of what hydroquinone is, not because it is small.

That distinction is what most ingredient lists skip. Our guide to niacinamide during pregnancy covers what it does for pigmentation and oil.

What this means for your routine

If you want a routine built on this reasoning rather than on a label claim, start with the nātelle Morning Radiance Serum.

It uses tetrahexyldecyl ascorbate at roughly 1,130 Daltons rather than pure ascorbic acid at 176, a choice made because the larger molecule is more stable, gentler on reactive skin and far less able to cross into your bloodstream.

It sits in every kit from the First Trimester Kit through to the Postpartum Kit, and the reasoning behind every other molecule we use is laid out in our full ingredient list.

This article is general information, not medical advice. If you have a skin condition, are using a prescription treatment or are unsure about an ingredient, speak with your GP, obstetrician or dermatologist. In Australia you can also call MotherSafe on 1800 647 848.