Formulating sunscreen is complicated, challenging and expensive. In the United States, cosmetics that claim an SPF are viewed as over-the-counter drugs and highly regulated. SPF (Sun Protection Factor) is a measure of a sunscreen's ability to prevent Ultraviolet B (UVB) rays from damaging the skin. Here's how SPF works: If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer, or about five hours.
Many natural, home-formulators try to formulate sunscreens by replacing proven sun protection ingredients with botanical oils. Why can’t you make a simple botanical oil sunscreen and be protected from the sun? Here are 3 reasons why botanical oils are no substitute for a properly formulated sun protection product with a verifiable and measureable SPF:1. Botanical oils don’t sufficiently absorb ultraviolet rays:
Researchers found that natural oils are not suitable UV-blocking ingredients. They measured the ultraviolet absorptivity of aloe vera, canola oil, citronella oil, coconut oil, olive oil and soybean oil and found that all of them did virtually nothing when it came to blocking ultraviolet rays. They concluded that their SPF would roughly equal SPF 1. This means that these ingredients do nothing to prevent reddening. 2. Botanical oils do not absorb ultraviolet rays at the correct wavelengths:
In the same study referenced above, Vitamin E was the only substance that showed appreciable ultraviolet absorbance, but this only occurred below a wavelength of 310nm which still allowed most of the UV spectrum to pass through unblocked. Sunlight’s UVB-UVA range is 290-400nm.3. Botanical oils have not had their SPF reliably tested or verified for use in sunscreen:
Natural botanical oils have not gone through the lab and human testing required to establish their respective SPF. Proper procedure follows:
- Start out by deciding what SPF you want to achieve in formulation and then choose the correct SPF blocker to get to that level.
- The formula is then tested in the lab multiple times during research and development to ensure that the SPF is still on track.
- The formula is then tested on human volunteers who are exposed to a specific amount of sunlight and their skin reaction is assessed.
- The lab compares these results with their test results to ensure the SPF matches.
This level of testing has not occurred for any botanical oils. If your materials supplier is selling botanical oils with a stated SPF, you should request a copy of their test results verifying these numbers. If they cannot provide the results, the SPF is not verifiable and you will need to test them before making any claims.
There are various botanical oils mentioned online by DIY formulators as “natural sunscreen”, and most of them have claimed to have an SPF. One of the most popular references is raspberry seed oil, with claims of SPF 30-50. Carrot oil, another natural botanical ingredient, is proclaimed to have an SPF around 38-40. At the lower end of the spectrum, you have coconut oil with a purported SPF of 8.
At face value, the claimed natural SPF of the first two oils is pretty amazing. In addition, natural oils have fantastic spreadability (meaning fewer missed spots during application), are very nourishing and come with a range of skin benefits like antioxidant content.
Not to be the raincloud at your beach party, but we would be remiss if we failed to point out the fact that these natural oils have not gone through testing to verify these SPF claims or even to determine whether they suffice as adequate sun protection.
The only true research verifying the supposed SPF of raspberry seed oil is a study reporting that “raspberry seed oil showed absorbance in the UV-B and UV-C ranges with potential for use as a broad spectrum UV protectant.” This seems promising, but again, it’s one study and the “potential” still stands to be tested and verified. 
What about carrot seed oil with its claimed SPF of 38 to 40? It turns out this belief of carrot seed oil having natural SPF is based on a study not of carrot seed oil, but of a sunscreen formula containing extracts of carrot, other botanicals and zinc oxide. The zinc oxide is likely the cause of this product’s SPF, not the carrot extract. As for the actual SPF of carrot seed oil, there is no reliable documentation measuring this.
Natural botanical oils are not adequate replacements for verifiably tested commercial sunscreen preparations. There is a plethora of options available for chemical-free, natural sunscreens that use physical sunscreen filters like zinc and titanium oxide to effectively protect skin from both UVA and UVB rays.
Botanical, antioxidant-laden, natural oils can help protect your skin against the free radical damage that comes with UV radiation. Slather them on liberally before you go out in the sun, as an after-sun moisturizer, or add it to commercial sunblock to give it an antioxidant boost. You’ll get an extra dose of antioxidant skin protection, but do not use botanical oils as a substitute or advertise them as a substitute for sunscreen.References:
- Gause S, Chauhan A. UV blocking potential of oils and juices. Int J Cosmet Sci. 2015 Nov 27. doi: 10.1111/ics.12296. [Epub ahead of print] PubMed PMID:26610885.
- Kaur, C. D., & Saraf, S. (2010). In vitro sun protection factor determination of herbal oils used in cosmetics. Pharmacognosy Research, 2(1), 22–25.http://doi.org/10.4103/0974-8490.60586
- B.Dave Oomah, , Stephanie Ladet, , David V Godfrey, , Jun Liang, , Benoit Girard. Characteristics of raspberry (Rubus idaeus L.) seed oil. Food Chemistry, Volume 69, Issue 2, 1 May 2000, Pages 187-193.