Last year I posted a sun block lotion and powder. This season I have been using a mix of oils and only using the block when I plan to be outside a long time.
The SPF rating is a measure of "how long a sunscreen remains effective on the skin."[19] The effectiveness of a sunblock can be determined "by multiplying the SPF factor by the length of time it takes for him or her to suffer a burn without sunscreen." [20]
Mathematically, the SPF is calculated from measured data as
where 
is the solar irradiance spectrum, 
the erythemal action spectrum, and 
the monochromatic protection factor, all functions of the wavelength 
. The MPF is roughly the inverse of the transmittance at a given wavelength.
is the solar irradiance spectrum, the erythemal action spectrum, and the monochromatic protection factor, all functions of the wavelength . The MPF is roughly the inverse of the transmittance at a given wavelength.
The above means that the SPF is not simply the inverse of the transmittance in the UV-B region. If that were true, then applying two layers of SPF 5 sunscreen would be equivalent to SPF 25 (5 times 5). The actual combined SPF is always lower than the square of the single-layer SPF.
Most oils have different degrees of protection. (COLD PRESSED ALL NATURAL OILS WILL HAVE HIGHER SPF PROTECTION THAT THEIR PROCESSED COUNTERPARTS)
The following is a partial list of some organic oils and their properties:
| Oil | SPF |
| Raspberry Seed Oil | 28 to 50 |
| Carrot Seed Oil | 38 to 40 |
| Argan Oil | 30 |
| Wheat Germ Oil | 20 |
| Avocado Oil | 4 to 15 |
| Soybean | 10 |
| Peppermint Essential Oil | 7 |
| Macadamia Nut | 6 |
| Coconut Oil | 2 to 8 |
| Lavender Essential Oil | 6 |
| Sesame Seed Oil | 6 |
| Aloe Vera Oil | 6 |
| Almond Oil | 5 |
| Shea Butter | 4 |
| Jojoba | 4 |
| Grape Seed Oil | 4 |
| Hemp Oil | 4 |
| Olive Oil | 2 to 8 |
The other thing to consider is the water resistant qualities of the oils you use, for example argan and sesame both soak right into the skin, they have a very fast absorption rate while coconut oil and shea butter take a while to absorb. You can also add beeswax or floral wax to make your formula more waterproof. It's all up to you!
I put together a small bottle of potent oils to use when I want to tan but not burn.
I used:
- 2 parts coconut oil
- 1 part argon oil
- 1 part red raspberry seed oil
Melt the oils together stirring them into one another. Pour into a serum container. A little goes a long way! About a 30 SPF.
You can also add a scent to it if you want. I didn't because we have too many bugs around here! If I add a sweet scent I know I'd be a target for every bee and wasp in the area! :) I thought about adding an essential oil from the mint family to repel the bugs but this round I left mine unscented. Try some and see! It works really well for about 1-2 hours, then it needs to be reapplied. I gave mine a good work out this weekend at the amusement park!
Happy sunning!!!
Marla Riedling
MJR Soaps
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