Hi Stephen! Why are certain ferments beneficial for our skin while others like plain alcohol are not? Thank you – Joan

Hey @jxxn!

It depends on what part of the fermentation we’re isolating. Ethanol is the pure alcohol that’s a product of fermentation, whereas a ferment lysate used in cosmetics is generally the entire system (lysate means that the cell walls have been ruptured).

It’d be like comparing yogurt (a mixture) to lactic acid (a pure substance).

The yeast used in brewing is filtered out of the final product and sold as a nutritional supplement, brewer’s yeast. Brewer’s yeast is rich with B vitamins, minerals, and proteins.


On the left is unfiltered beer, and on the right is filtered beer.

Hope that helps!


For everyday sunscreen, how high should the PPD (UVAPF) be? I’ve been on the hunt for a new sunscreen, so I’ve been thinking about this a lot!

Hi @wormspoor,

Thanks for the question! I’d recommend that SPF and UVAPF are similar. So if a product’s SPF is 30, the UVAPF should be around 30 as well.

Why? This best mimics the reduction in UVA and UVB that shade provides.


As well this gives you a better idea of how much protection from the entire UV spectrum you’re getting. Imagine you’re using a sunscreen with SPF 50+, but only UVAPF 10. While you’re not sunburning, you’re still exposed to a good amount of UVA energy – this is why people are often confused when they develop a tan despite wearing a very high SPF.

P.S. PPD is just one of the methods used to determine UVAPF, it involves human subjects and compares how much protected vs unprotected skin darkens. Other methods involve measuring transmittance in the UVA wavelength bands.


Hi Stephen! I love your work, I’ve been using the Bioderma Photoderm, partly because of your recommendation

…but I can’t seem to get rid of the white cast. I know you shouldn’t mix mineral powders with sunscreen, but is there any reason I can’t mix unadulterated cocoa powder with it to create a tint? Thanks for any thoughts!


I’d really advise against this. Part of the protection offered by sunscreen is how evenly they can distribute the sunscreen chemicals on the skin.

Think of a crowd of people with umbrellas in the sun. If they’re all evenly distributed, very little sunlight will hit the ground…but if they’re clumped together, there’ll be more areas where the sunlight can pass through.


Sunscreen chemicals work in a similar way.

By mixing something like cocoa powder into a sunscreen, you can create areas of high sunscreen chemicals and low sunscreen chemicals – creating uneven coverage. Manufacturers use mixers with high shear and force to make sure everything is distributed properly.

If you’re getting a white cast, I think the best way to fix it is to apply your sunscreen…allow it to dry (15 minutes), and then apply a foundation or tinted powder on top!

Bioderma (and many other sunscreen brands) also makes tinted versions of their sunscreen, so you don’t have to worry about the white cast or uneven mixing!

I personally also use their mineral sunscreen compact, it comes in two shades (Claire/Fair and Doree/Golden). I’ll sometimes use the Fair all over, and Golden as bronzer/contour. Shiseido also offers a UV Protective Compact in 9 shades, that you can layer on top of your sunscreen. Hopefully you can find a shade that works for you, if not, a foundation powder with SPF like BareMinerals Ready SPF 20 Foundation will work as well.

I’ve shared an experiment before about titanium dioxide and pigments destabilizing avobenzone, however this is more important for manufacturers as the degradation takes course over a long period of time (1 week in the experiment) and requires constant UV exposure.

P.S. I wouldn’t recommend using a compact as your only sun protection, you still need the recommended 2mg/cm2, and it’s more difficult to gauge how much you’re applying when it’s coming off of a pan!

Hope that helps 🙂


I’m wondering if you have suggestions for skin care stuff that doesn’t get interact weirdly with body hair

….I’m a hairy person and I find moisturizer gets sticky in my it and exfoliants get caught in it, especially on my legs and stomach

That’s a great question and a tough one to answer! I hope you’ll find my suggestions useful though.

The first thing you can try is using your current moisturizer right out of the shower, before toweling dry, while your skin is still wet. The extra water will help lubricate the skin and hair. Skin tends to absorb lipids better when saturated with water as well!

Another thing to think about is whether or not your cleanser is too much for your skin. Cleansers are one of the few times we actually remove lipids and moisturizers out of the skin. You could look for an oil-based cleanser, like Eucerin pH5 Skin-Protection Shower Oil. You may find with a less powerful, and more lipidic cleanser – you don’t need to moisturize after showering.


In terms of your exfoliant, if it has got beads in it – there isn’t really much you can do. You could try an exfoliating textured towel (Salux is a popular Japanese brand) or a brush or shower puff – but it’s probably going to pull on your hair and hurt a bit.

I think best would be a moisturizer with a exfoliating acid (applied to wet skin) or perhaps a body wash with an exfoliating acid in it. If you go with a body wash, you’ll want to let it sit on the skin for 30 seconds or more, so the acid has time to work.

An exfoliating moisturizer I’ve used and liked is the Neostrata Body Smoothing Lotion with 10% Glycolic Acid. I’m not sure about its global availability, so forgive me if you can’t find it. Paula’s Choice RESIST Revealing Body Lotion with 10% AHA may be worth looking into as well, I personally haven’t used it.

Look for keywords like “Glycolic Acid”, “Lactic Acid”, “AHA” or, “Alpha Hydroxy Acid”.

An exfoliating acid also has the benefit of being better for the environment, as synthetic microbeads are being recognized as a water pollutant.

I’d also suggest trying in-shower moisturizers, they’re similar to regular moisturizers and creams except they have a lower water content (The water comes from your wet skin!). As the name suggests, you apply them while you’re still in the shower.

Olay, Nivea, and Eucerin all produce in-shower moisturizers now.

If you don’t like being damp, a spray moisturizer may be worth trying.

You could look for Vaseline’s Spray and Go and St. Ives Fresh Hydration canisters.

Lastly, you could try trimming your body hair, but that’s probably not worth it 🙂

I hope that helps!


Hello! I just found your blog and I really love it! And I already have a question. :)

… Basically I have a question about the last question you got. The person who asked mentioned that we’re required to use 1/2 teaspoon of sunscreen for the face alone and now I’m a little confused because I’ve thought that we “only” need 1/4 of a teaspoon? Or about 1.25 ml? Is that wrong? I’m sorry for asking, I’m just always worried about not using enough product to get the proper protection.

Great question, thanks for asking @naevery 🙂

It’s not right, and it’s not wrong…it depends!
Let me explain 🙂

The density of sunscreen used in SPF testing is always 2 mg/cm2

That means for every square centimeter or skin, 2 mg of sunscreen is applied.

This is easier to do when testing, because it’s done on the back where you can draw a 30 cm2 square and apply 60 mg to it.

Figuring out the area of the face is trickier.

The ¼ teaspoon or ½ teaspoon or 1.25 ml are based on two estimates.

The first estimate is the average area of a human face, and the second estimate is the average density of a sunscreen. Remember that ml is a measurement of volume, it provides no information about weight.

Water at 4°C has density of close to 1. 1 ml of water will weigh about 1 mg. However, oil for example has a lower density, 1 ml of oil won’t weigh 1 mg, it might weigh 0.8 mg (depending on the type of oil).

That makes things more complicated, because you can’t assume that 60 ml of sunscreen will weigh 60 mg, it might weigh 65 mg or 55 mg.

So the ¼ teaspoon, or ½ teaspoon are just estimates for an estimated human face, and an estimated sunscreen density.

These researchers for example used a beer bottle cap to measure out sunscreen.

So in order to know how much sunscreen, exactly, to apply you’ll need two measurements. The density of your sunscreen, which you can take by measuring out, say, 10 ml of sunscreen then weighing it. You’ll probably want a jewelry scale that has 0.001 g accuracy, and to measure a few times and average your measurements!

Finding out the area of your face is more difficult.

There are studies where people are told to apply sunscreen, and how much they’ve applied is weighed. It usually ranges between 0.5-1.5 mg/cm2, when they’re unprompted about applying 2mg/cm2. Their recommendation is to have people apply their sunscreen twice, instead of worrying about ¼, ½ teaspoon.

It’s up to you to how you decide to apply your sunscreen. Whether it be weighing it, measuring out the volume, or applying it twice, it’s better to err on the side on more for sun protection!

For Reference: ml = milliliter, mg = milligram, cm = centimeter, g = gram, and 1 mg = 0.001 g

Hope that helps!

Hi Stephen, I had a question for you about the UV protection in products like tinted moisturizers

…foundations, BB and CC creams. I see that they’re rated as highly as the straight sunscreens/sun creams. Theoretically, if we used the required 2mg/cm2 (1/2 tsp) of these products for the face, will they give the same level of protection as the straight sunscreens/creams? I’m asking because I’m wondering if I could be relying on a watery serum foundation for the entirety of my sun protection.

Yup! Anything that has an SPF is tested the same way.

While the US FDA, Colipa/ISO methods have a couple differences, it is always at the density of 2mg/cm2.

As long as it has an SPF rating, and you’re applying it at that density, you can be assured you’re getting that SPF – whether it’s called a serum, moisturizer, sunscreen, face pack, you name it!

Note of Interest: Only people with Skin Types I, II, or III are eligible to participate in the US FDA’s sunscreen testing protocol.

(I) Always burns easily; never tans (sensitive).

(II) Always burns easily; tans minimally (sensitive).

(III) Burns moderately; tans gradually (light brown) (normal).

Thanks for the question 🙂