Afshine Emrani MD FACC@afshineemrani
I need to talk to you about what's in your sunscreen — because an FDA-funded clinical trial proved something in 2020 that most people still don't know.
Six of the most common chemical sunscreen ingredients — oxybenzone, avobenzone, octocrylene, homosalate, octisalate, and octinoxate — are absorbed through your skin and into your bloodstream after a single day of use. This was published in JAMA. Not a wellness blog. The Journal of the American Medical Association.
The FDA's own safety threshold is 0.5 nanograms per milliliter. Oxybenzone reached plasma concentrations exceeding 200 ng/mL — roughly 400 times the threshold that would normally trigger mandatory safety testing. Some ingredients were still detectable in the blood 21 days after the last application.
Oxybenzone is a documented endocrine disruptor. It mimics estrogen in the body. It has been detected in 97% of Americans tested by the CDC. It crosses the placenta. It has been found in breast milk and amniotic fluid.
The FDA's response to its own study: continue using sunscreen while manufacturers conduct additional safety research.
That was six years ago. The additional safety data from manufacturers has still not been submitted.
I want to be precise about what this means and what it doesn't.
This does NOT mean sunscreen causes cancer. UV radiation is a proven carcinogen. Unprotected chronic sun exposure increases skin cancer risk. That science is settled. I am not telling you to stop protecting your skin.
But it DOES mean that the specific chemicals in most commercial sunscreens enter your bloodstream at levels that were never proven safe — and that safer alternatives already exist.
Here's what most people don't know: mineral sunscreens — zinc oxide and titanium dioxide — are classified by the FDA as GRASE: generally recognized as safe and effective. They sit on the surface of the skin and physically block UV radiation. They are not absorbed into systemic circulation. They don't disrupt hormones.
They cost more to manufacture. They can feel thicker on the skin. And they represent a small fraction of the market — because chemical sunscreens are cheaper to produce and easier to formulate into the cosmetically elegant products consumers prefer.
Now the vitamin D piece — because this is where my practice as a cardiologist intersects directly.
I've written extensively about vitamin D on this platform. Most Americans are deficient. Low vitamin D is linked to higher cardiovascular risk, weaker immune surveillance, increased inflammation, and poorer outcomes across nearly every chronic disease I treat.
Your body manufactures vitamin D only when UVB radiation hits bare skin. Fifteen to twenty minutes of direct sun exposure on your arms and face — before applying sunscreen — can produce 10,000 to 20,000 IU of vitamin D naturally. That's the dose you'd need to take in supplement form to match what your body makes for free.
Chemical sunscreens block the exact UVB wavelengths that drive vitamin D synthesis. This isn't a conspiracy — it's photochemistry. If you apply chemical sunscreen before any sun exposure every single day, you are reducing your body's ability to produce vitamin D. The solution isn't to abandon sun protection. The solution is to get brief, intentional sun exposure first — then protect.
Here's what I actually recommend to my patients:
Get 15-20 minutes of morning sunlight on bare skin before applying anything. Arms, face, no sunglasses. This drives vitamin D synthesis and resets your circadian rhythm.
When you need extended sun protection, use a mineral sunscreen — zinc oxide or titanium dioxide based. Look for "non-nano" formulations. They stay on the surface. They don't enter your blood.
Check your vitamin D levels. Target 50-80 ng/mL — not the bare minimum of 30 most doctors accept. Supplement with D3 plus K2 if needed.
Read the label on your sunscreen the same way you'd read a food label. If it contains oxybenzone, avobenzone, octocrylene, homosalate, octisalate, or octinoxate — you now know these chemicals enter your bloodstream at levels the FDA itself flagged as requiring further safety evaluation. Safer options exist.
This isn't about fear. It's about informed choice. The same way I want you to know your ApoB, your Lp(a), and your hsCRP — I want you to know what you're absorbing through the largest organ in your body every day.
The FDA confirmed the absorption in 2020. The safety data still hasn't arrived. You deserve to make your own decision with both halves of the truth.
