A recipe I created after a lot of research and borrowing from many, many sources. It is a hybrid designed to be very durable in water and provide extreme protection against the sun. It contains PABA, to which some people have allergic reactions. If you are one of these, omit the PABA, but the protection won't be quite as good. It is so protective with the PABA that a fish-pale medical resident (myself) was able to stay out for 4-5 hours in the hot Belize sun while mostly swimming with only minimal obvious tanning. Results may vary depending on how thick you put it on and how sun-susceptible you are, and I in no way warranty or guarantee this formula, as that is just one data point.

This not cheap to produce, as the ingredients are expensive, particularly good quality shea butter, nor is it particularly easy to actually make, as it requires a good-quality 1000ml beaker or something similar (could use a 1 qt saucepan), a good-quality liquid measuring device (such as a 150ml graduated cylinder), a good-quality thermometer, an appropriate stirring device (such as a metal whisk or Pyrex or similar rod), a scale for weighing powder in gram weights accurately, a good-quality fine-particle-blocking face-mask, and the care and skill required to work with hot liquids and fine powders safely. You will also need light-blocking storage jars (2oz-8oz sizes work well for this).

In a Pyrex or similarly heat-resistant 1000ml beaker or pot that is sitting in a stable water-bath over medium heat (preferably electric) at a temperature of somewhere just above the melting point of beeswax, which is about 145F/63C, so about 160F/71C, and using a quality thermometer to keep it there so that mixture will stay liquid while you work, but also making it no hotter than it needs to be (as it will increase the oxidization of the oils and also make it more dangerous to work with) and being very careful not to burn yourself, add to the beaker:

Coconut Oil 3oz/90ml
Cocoa Butter 2oz/60ml
Shea Butter 3oz/90ml
Beeswax 0.75oz/22ml
Vitamin E mixed tocopherols 0.75oz/22ml
Almond Oil 4oz/120ml
Jojoba Oil 2oz/60ml
Sesame Oil 1oz/30ml (not toasted oil, just the light, clear stuff)
Avocado Oil 1oz/30ml

Nearly everything that went into mine was organic, but you can be less tweaky as your needs and budget allows. It has a somewhat nutty smell due to the sesame oil, but can easily take essential oils to scent it (but avoid those that are sun-sensitizing). You could substitute more jojoba oil for the sesame oil if you don't want it to smell like sesame.

Then, and here is the first tricky part, mix in a separate small container as best you can 1oz of lecithin with 30g PABA.This will make a sticky, orange mess. You might need to add just a bit of water, say a few ml but no more. Mix this mixture thoroughly into the oil mixture in the beaker, but avoid splashing or burning yourself. It will not be easy to get it to mix in well at this point. There will be time later when the mix is cooling and is stiffer to mix it in better.

Why PABA? This amount of PABA will make the final mix about 1/18th part PABA, giving an SPF slightly less than 15 in theory, and provides solid UVA protection, but not UVB protection. See here for more on UVA, UVB, and what blocks them and why.

Next, put on a good-quality fine-particle-blocking face-mask, and measure out 33g of Ultra-Micronized Titanium Dioxide (an annoyingly fine powder), available at various on-line suppliers (as is the PABA), making a final concentration of about 6%, which gets you to about SPF 12-19 in theory. Putting a plastic bag on the scale may help reduce scatter somewhat. Pour very slowly, as it tends to want to go everywhere. Then very carefully add the Titanium Dioxide to the oils in the 1000ml beaker and stir carefully and slowly so it doesn't make a huge powdery mess. It should be noted that recently (after I made this initial recipe) the safety of very fine nano-particles of Titanium Dioxide has been called into question. I refer you here for more on that. How safe is it? I can't find a clear answer. On the other hand, UV radiation is known to be quite harmful. You make your own risk-benefit analysis and proceed based on your own judgement and assume your own risk. There are other things you can put in the base for a similar effect, such as zinc oxide. I will leave the fine points of any such innovations to you.

Cut the heat to the water bath and stir the mixture frequently as it cools, which will take a while, being careful not to splash or burn yourself on the hot sunscreen. This will help distribute the Titanium Dioxide and distribute the PABA more finely, though it will still tend to be a bit clumpy, though this disappears when applied. Transfer the liquid to light-tight storage jars (blue or brown glass, ceramic, metal, etc.) when cool enough to handle but still able to be poured. This is a good time to swirl in a few drops of any appropriate skin-safe, non-sun-sensitizing essential oils you care to add. Seal the containers and store them in a cool place. I know from experience that if you freeze them this stuff lasts at least 8 years, as that is how old mine is and it is still just fine.

Realize that even extremely high-quality sun-screen like this may not completely protect you from the damaging effects of UV radiation, so use appropriate caution. I have no idea what the SPF of this mix is, but in comparison to commercial preparations I have used it has bested them all and I had the deep satisfaction of knowing exactly what was in it and that I made it, which made it all worth it.

This mix is definitely somewhat oily-feeling when applied and relatively thick. Again, it was designed to be a high-performance, high-durability, highly-skin-nourishing sunscreen, and in my personal testing it performs as I designed it. I hope you have similar results, and if you have any comments or modifications to it, let me know.

Enjoy and be safe,

Daniel