Carrot Seed, Coconut, and Olive Oil SPF: The Real Numbers

Three oils get cited constantly as natural sun protection: carrot seed at SPF 38 to 40, coconut at around 7, olive at around 7.5. Two of those numbers are real measurements of something. None of them is an SPF. Here is where each figure came from, what was measured in each case, and why the distinction is the whole story.

Carrot seed oil: the SPF 38 number is not measuring the oil

This is the big one, and it is the one worth understanding properly. The claim traces to a 2009 paper by Kapoor and Saraf on the efficacy of sunscreens containing various herbs. Read the title again: sunscreens containing herbs. The sample that produced the high reading was a finished commercial sunscreen product that had carrot in it, alongside its other ingredients.

So the number describes a formulated sunscreen. It does not describe carrot seed oil. The paper does not even specify which carrot extract was used or what else was in the bottle. Somewhere between that study and the internet, a result belonging to a complete product got reassigned to a single ingredient, and it has been repeated ever since.

Carrot seed oil has never been tested as a standalone sunscreen on human skin and passed. It is not an FDA-approved UV filter. It is an aromatic oil with antioxidant content and no meaningful sun protection on its own.

Coconut oil and olive oil: real readings, wrong unit

These two come from a different and more honest place. A 2010 paper by Kaur and Saraf measured the UV absorbance of herbal oils in a spectrophotometer and reported coconut oil at 7.119 and olive oil at 7.549.

Those are genuine laboratory measurements. The problem is what they measured: how much UVB light passed through a diluted sample of oil in a machine, across the 290 to 320 nanometer range. That is a useful number for a formulator comparing raw materials. It is not SPF.

Why a spectrophotometer reading is not an SPF

SPF is not a property of a liquid. It is the result of a specific test on human volunteers, run under an FDA-standardized protocol: the product goes on real skin at two milligrams per square centimeter, the skin is exposed to controlled UV, and the point at which it reddens is compared against unprotected skin. The number that comes out reflects the whole formula behaving on real skin.

A machine reading skips everything that decides whether a sunscreen works in the world:

• Whether the film holds together. A UV filter only protects the skin it is evenly covering. Oils spread thin and pool unevenly.
• Whether it survives light. Photostability decides whether protection lasts twenty minutes or two hours. A cuvette in a dark instrument never tests that.
• Whether it survives water and sweat. There is a separate FDA test for that, and it is unforgiving.
• UVA. The 290 to 320 range is UVB only. UVA runs to 400 nanometers and is the part that drives ageing and pigment. It was not in the measurement.

We saw the size of that gap in our own testing. A DIY recipe made with 25 percent zinc oxide, more zinc than most commercial sunscreens carry, came back at SPF 13 static and SPF 7 after the 40 minute water test. That is with a real, FDA-recognized mineral active doing the work. An oil with no UV filter in it has less to offer than that, not more.

What SPF 7 would mean even if it were real

Suppose coconut oil genuinely delivered SPF 7 on skin. The FDA requires broad spectrum SPF 15 or higher before a product can carry the sun protection labelling that matters. SPF 7 sits below that line. And that is the generous reading, granting a number the test was never designed to produce.

There is a second cost that gets missed. Oil on skin in the sun feels like protection. It is occlusive, it looks glossy, it makes the skin feel covered. Someone who believes they are protected stays out longer and reapplies less than someone who knows they are bare. That is the part worth being blunt about.

Where Swellies fits

If the appeal of these oils is a short, readable ingredient list, that instinct is right. The conclusion just has to point somewhere that works.

Swellies is five ingredients, and all of the protection comes from one of them: 21 percent non-nano zinc oxide, one of only two actives the FDA has affirmed as generally recognized as safe and effective. It covers the full UVA and UVB range on its own, which no oil on this list does at any wavelength. Broad Spectrum SPF 46, water resistant 40 minutes, tested on human skin under the protocol that produces a real number.

The other four ingredients are there so the zinc behaves: a plant-derived ester carrier, a gel former, a dispersant that prevents white cast, and iron oxides for tint. Short list, and every item on it earns the place. More on why the seed oil claims keep circulating in seed oils have no meaningful SPF.

Frequently asked questions

Does carrot seed oil have an SPF of 38?

No. That figure comes from a 2009 study that tested a finished commercial sunscreen product containing carrot alongside its other ingredients, not carrot seed oil on its own. The result describes the formulated product. Carrot seed oil is not an FDA-approved UV filter and has not passed a standardized SPF test as a standalone sunscreen.

Does coconut oil have SPF?

Coconut oil was measured at 7.119 in a 2010 in vitro study, meaning UV absorbance of a diluted sample in a spectrophotometer across the UVB range. That is not an SPF. SPF is measured on human skin under an FDA protocol, and coconut oil has not been shown to provide meaningful sun protection when used that way.

What is the SPF of olive oil?

The same 2010 in vitro study reported olive oil at 7.549. Like the coconut oil figure, it is a laboratory absorbance reading rather than a tested SPF, and it covers only UVB. It should not be relied on for sun protection.

Why is in vitro SPF different from real SPF?

An in vitro reading measures how much UV passes through a sample in an instrument. A real SPF test applies the product to human skin at a set dose and measures when the skin reddens under controlled UV. The instrument version skips film formation, photostability, water and sweat resistance, and UVA above 320 nanometers. Those factors decide whether a sunscreen works.

Can I mix these oils with zinc oxide to make sunscreen at home?

Mixing is the failure point, not the ingredients. We had a DIY recipe with 25 percent zinc oxide tested at an FDA-approved lab and it returned SPF 13 static and SPF 7 after the 40 minute water resistance test. Zinc has to be dispersed evenly to protect evenly, and a kitchen blender cannot do it reliably. You also have no way to know what you ended up with.

What should I use instead?

A sunscreen with a real tested SPF and a UV filter the FDA recognizes. Zinc oxide is the only single mineral active that covers the full UVA and UVB range on its own, which is why Swellies uses it as the only active at 21 percent.

Five ingredients. One active. A number that came from a real test. See Swellies →