Sunscreen dosing. Teaspoons, shotglasses, and fingers…are we using too much?

Sunscreens and moisturizers with SPF are tested at a standardized density. That density is 2 milligrams of sunscreen per square centimeter of skin. If we want protection closer to what’s on the label, we should be using sunscreen or moisturizers with SPF at the density they’re tested at too.

Most of us don’t know the surface area of our skin and most of us don’t know the density of our sunscreens either. This has led to techniques and recommendations, like using 2 or 3 finger lengths of sunscreen, using 1/4 teaspoon of sunscreen, or applying our sunscreen twice. These techniques are all meant to encourage a more generous application of sunscreen, because when unprompted people tend to not apply enough.

With sunscreen, I think it is better to err on the side of applying too much rather than not enough. A higher density and thicker film of sunscreen generally means higher protection. It also makes sense to use more, because some of the sunscreen we apply will remain on our fingers, palms, or tools.

In some cases, I think these techniques might be leading people to use much more sunscreen than they might need. A sunscreen that might have been acceptable at a lower density might leave a strong cast, be too greasy, or pill (when a formula adheres to itself and rubs off the skin). This is especially relevant for people with deeper skin tones evaluating sunscreens for cast.

I’ve made a rough estimate of the surface area of my face, as well as the density (grams per millilitre) of two different sunscreens (IGTV: ‘How much sunscreen do you need?’). One is a cream and the other is a free-flowing milky texture. For both sunscreens, I need about 0.8 millilitres (mL) of sunscreen to get about the 2 milligrams of sunscreen per square centimeter of skin for my face. If I used a 1/4 teaspoon (1.23 mL), I’d be dispensing about half more than I need to protect my face.

With the cream sunscreen, applying 3 finger lengths of sunscreen dispensed about 3 mL of sunscreen. That’s almost 4 times more sunscreen than I might need. With the milk sunscreen, applying 3 finger lengths of sunscreen dispensed about 1.5 mL of sunscreen. That’s about 2 times more sunscreen than I might need. There’s also going to be differences in the thickness of our ‘lines’. That depends on things like how hard we squeeze, how slow we dispense, and the packaging.

If I apply the milky sunscreen with my palms and fingers the amount that ends up on my face might be close to the density I need. With 3 fingerlengths of the cream sunscreen, the finish is greasy and leaves a strong cast. The sunscreen is unusable for me with this much. But If I apply around 0.8 mL of the cream sunscreen, the finish is much nicer and I don’t notice a cast.

There’s no right or wrong method, they’re all just recommendations to encourage “proper” sunscreen use. Measuring your skin’s surface area, sunscreen density, and then each dose is going to be impractical for most people. But we might think about taking another look at sunscreens that may have been overused and left an unusable finish. They might not have at a density closer to the one it was tested at.

A photo showing 3 fingerlengths of a liquid, runny and milk appearing sunscreen. A photo showing those 3 fingerlengths of the milk appearing sunscreen collected in a syringe. It amounts to about 1.5 mL of sunscreen.

A photo showing 3 fingerlengths of a cream sunscreen. A photo showing those 3 fingerlengths of the cream sunscreen collected in a syringe. It amounts to about 3 mL of sunscreen.

One of the ways we can encourage use of sunscreen is modeling realistic use. Many people can’t stand wearing heavier coats of sunscreen, and that’s OK. Some sun protection is better that none.

On the opposite end, brands need to take responsibility for their marketing, and show actual and proper use – especially since they’re the ones testing it at the right density. A smidge might look nice in an advertisment, but we all know it’s not enough and misleading. In the US, sunscreens are drugs not cosmetics – brands need to respect that and stop playing around.

Cheers to @FiddySnails for popularizing the 2 and 3 finger methods. They work for her because her 3 finger-lengths are not as chonky as mine. As well, when using 3 finger-lengths she uses a cushion puff to apply – which is absorbing some of the sunscreen.

If they made 1/6th teaspoons, I’d be golden. You don’t need to overthink this like I did! Our first application of sunscreen doesn’t need to be “perfect” if we reapply throughout a very UV-exposed day. All these techniques, besides precise measurements, are just estimates or rules of thumb – so some common sense and adjustments are sometimes needed!

Skincare Optimizing and Anxiety: Unrealistic expectations of perfection from imperfect information.

I often get emails like the following:

“I use X sunscreen, after 15 minutes, I use a foundation.

The ingredients of X sunscreen are Drometrizole Trisiloxane (Mexoryl XL) 7%, Bemotrizinol 5%, Octisalate 5%, Octocrylene 5%, Avobenzone 3%, Homosalate 2%, Ensulizole 0.5%

The makeup contains Octinoxate 6.0%, Titanium Dioxide 3.8%, Zinc Oxide 3.0%.

Will this destabilize the avobenzone or affect the SPF protection?”

Usually, my response is that it’s impossible to know just based on the ingredients alone.

We need to be able to measure the changes we’re interested in. In this case with an SPF test performed on humans and a photostability test.

This is the only answer that isn’t completely hypothetical.

That’s how I respond, and almost every time there is a follow up question:

“If I used this sunscreen without avobenzone, would that be better? Should I change the makeup I am using? Should I wait longer between applications? Would that be better?”

I think this anxiety is partly due to a growing amount of science-washing in the beauty community.

People, brands, and retailers sometimes describe skincare down to an unrealistic level of precision and accuracy. Using scientific terminology, biochemistry, and statistics in a way that almost becomes untruthful or irrelevant.

But what’s most important is the removal of context. Experiments often simplify reality to their most relevant parts, and their results shouldn’t necessarily be extrapolated.

Scientific literacy isn’t just about recognizing and understanding equations, keywords, or jargon.

It’s also the ability to recognize what is being discussed and what isn’t, how it fits into the larger context, and when to apply or not apply new information.

This is the same with medical literacy. Yes, we have access to more medical information than ever before, but we don’t necessarily have the experience, or critical skills to diagnose or treat ourselves.

To people who have anxiety about whether they’re getting the “most” out of their skincare products, be they sunscreen or otherwise, I think these two thoughts are important to keep in mind…

It is impossible to “optimize” or “maximize” something if you can’t measure it.

Some is better than none.

How to recycle cosmetics through TerraCycle in the US, Canada, the UK, Australia, New Zealand, and Brasil

Recycling is one of the ways we can mitigate part of the impact we have on the environment. Reducing and reusing are the better options, but sometimes waste is unavoidable.

I’ve noticed a few people in my life prefer skincare and beauty products that either come in squeezable tubes or come in pump bottles. They’re often easier to dispense and use. Unfortunately, depending on where you live, your local home recycling may not accept these types of packaging – even if the materials themselves are recyclable. Many pumps contain a metal spring which means it is mixed material, in Toronto that means it goes into the garbage. Even if you take the extra step of removing the spring, the plastic pieces are too small to be accepted into Toronto’s recycling stream.

You should always check with your local recycling collection to see what types of material and products can or can’t be recycled from your home.

A recycling logo doesn’t necessarily mean you can put it in your recycling. Check on your city’s recycling website first. Don’t just wishfully recycle, that can cause clogs and contamination, creating even more waste.

For example in Toronto, New York, and Seattle stiff plastic bottles are recyclable, but plastic squeeze tubes are not accepted. However, Chicago will accept plastic squeeze tubes and all sunscreens — even sprays!

Don’t dismay, some stores will offer recycling for harder to recycle items like plastic bags and electronics.

TerraCycle has partnered with a few companies to provide a way to recycle most cosmetic packaging.

United States

In the US, all brands of beauty products and packaging can be dropped off at Deciem and Nordstrom stores.

For the list of Deciem stores:

For the list of Nordstrom stores:

In the US, all brands of beauty products and packaging can be mailed in through a program sponsored by Garnier.

The minimum weight of each shipment must be 15 pounds.

To sign up for a shipping label:


In Canada, all brands of beauty products and packaging can be dropped off at Deciem and Holt Renfrew stores.

For the list of Deciem stores:

For the list of Holt Renfrew stores:

United Kingdom

In the UK, all brands of beauty products and packaging can be dropped off at Deciem and Maybelline drop-offs.

For the list of Deciem stores:

For the list of Maybelline drop-offs:


In Australia, all brands of beauty products and packaging can be dropped off at David Jones locations.

For more information:

New Zealand

In New Zealand, all brands of beauty products and packaging can be mailed in through a program sponsored by Garnier.

To sign up for a shipping label:


In Brasil, all brands of beauty products and packaging can be dropped off at Natura and The Body Shop locations.

For the list of locations:

TerraCycle does offer other recycling partnerships in other countries that I haven’t listed here.

To check if your country has a program visit or

Find your country, click through to ‘Free/National Recycling Programmes’ and browse through ‘All Recycling Programmes’.

Understanding Sun Protection Labels

SPF, PA, PPD, UVA, Stars…What does it all mean?

Sun Protection Factor (SPF)

The SPF number is a ratio of how much UV exposure your skin can be exposed to with the sunscreen on compared to without. The SPF test uses erythema or sunburn as a marker, which is mostly caused by UVB.

Hypothetically, an SPF 30 would mean you can be exposed to 30 times more sunburn causing UV compared to without the sunscreen on.

SPF 30 does not necessarily mean that you can stay out 30 times longer in the sun before sunburn. That is because the amount of UV coming from the sun is not always the same.

Broad Spectrum

Broad spectrum is a statement on how a sunscreen absorbs different wavelengths of UV light.

While the label requirements differ between regions, they all must meet a minimum critical wavelength of 370 nanometers.

That means when measured, at least 90% of the UV light the sunscreen absorbs is below the wavelength of 370 nanometers.

Broad spectrum is a signal that the sunscreen offers better UVA protection than a comparable sunscreen without the label.

UVA Circle

The UVA Circle symbol means that the sunscreen’s UVA protection is at least a third of the SPF.

If a sunscreen with the UVA Circle symbol has an SPF 30, you can expect a UVA 10 or higher.

The UVA Circle symbol does not tell you the exact UVA protection, just the minimum you might expect.

UVA Protection Factor

The UVA number (sometimes UVAPF number) is a description of how protective a sunscreen is against UVA radiation.

The UVA number is a ratio, like SPF. A UVA 30 means hypothetically you can be exposed to about 30 times more UVA with proper application of the sunscreen than without.

The UVA number can be determined in vitro (non-human testing) by measuring and comparing the amount of UVA light that passes through the sunscreen on textured plastic.

The UVA number can also be determined in vivo (human testing) with persistent pigment darkening or PPD.

Persistent Pigment Darkening (PPD)

The PPD number is a ratio of how much UV the skin can be exposed to before developing a long-lasting tan with the sunscreen on compared to without. Long lasting tans are mostly caused by UVA.

PPD is tested for on people with Fitzpatrick Skin Types 2 to 4 and mostly measures the effects of UVA.

Hypothetically, a PPD 10 would mean you could be exposed to 10 times the UVA with the sunscreen on, compared to without.

PPD results are sometimes labelled as UVA or UVAP. To find out, contact a brand’s customer service and ask which method they used to determine their UVA or UVAPF number.


The PA system ranges from + to ++++ and is based on values from PPD. It was developed in Japan and used in countries like South Korea.

PA+ = PPD 2 to 4
PA++ = PPD 4 to 8
PA+++ = PPD 8 to 16
PA++++ = PPD 16 or greater

The PA system runs into issues when comparing sunscreens with higher PPD numbers. For example, a PPD 20 and PPD 25 sunscreen would both be labelled as PA++++.

Boots Star Rating

The Boots Star Rating is a UVA rating system used by the British retailer Boots.

It describes the ratio of the UVA to UVB absorption of a sunscreen and is tested in vitro (not on people.

The test compares the ratio before and after UV exposure, which accounts for the sunscreen’s photostability.

PRE 0.6 to 0.79PRE 0.8 to 0.89PRE 0.9 and over
POST 0.57 to 0.75* * ** * ** * *
POST 0.76 to 0.85* * ** * * ** * * *
POST 0.86 and over* * ** * * ** * * * *

Getting what’s on the label

Most people don’t apply enough sunscreen when unprompted. To get close to the protection label on the sunscreen, the recommended amount is 2 milligrams per square centimeter of skin (2 mg / cm2).

There’s many different techniques to increase the amount of sunscreen you use. The one I prefer and do most often is to apply it twice, with an aim to reapply at least once during an outdoor day.

We don’t need to stress out too much about the exact amount we’re applying…more is generally better and reapplication can make up for a first application.

The best sunscreen is the one you enjoy using consistently, often, and liberally.

How common are allergies to sunscreen?

“25 percent of all people are going to be allergic to chemical sunscreens.”

This statistic was published in a beauty magazine recently.

Contemporary experiments and surveys have been done on the topic of sunscreens as an allergen. Here are the conclusions of some of them…

“Of 23,908 patients patch tested, 219 (0.9%) had sunscreen coded as an allergen source. “

“Allergy to sunscreen represents a small proportion (< 1%) of allergic contact dermatitis reactions in North America”

“[Allergic contact dermatitis] to sunscreen was found to be very uncommon (0.8%).”

There are more papers on this subject, but all their results have a common trend. None of them estimate rates of allergies to sunscreens or sunscreen chemicals for the general population to be even close to 25%.

Most found an allergy to sunscreen’s prevalence among patients with conditions like photosensitivity to be less than 1%.

That’s patients, people who had some kind of skin reaction and went to a doctor — for the general population the prevalence is probably even lower.

Analysis of the Prevalence of Allergic Contact Dermatitis to Sunscreen: A Cohort Study
By Katie Beleznay, Gillian de Gannes, Sunil Kalia
Published January 1, 2014

In this experiment they reviewed 1,527 patients who were tested against 70 allergens.

23 of those 1,527 patients were further tested against sunscreen chemicals. Of those, only 4 patients reacted. 8 other additional patients of the 1,527 tested patients reacted to oxybenzone.

The quoted 25% likely came from a misframing like this, the prevalence of allergy they found is not 4 out of 23 patients (17%). It’s 12 out of 1,527 patients (0.8%), and likely lower for the general population.

“The prevalence of positive patch test reactions to sunscreen chemicals or a sunscreen product was 12 of 1,527 (0.8%) for all patients referred to our clinic for patch testing.

Other data indicate that among patients referred for patch testing, the prevalence of allergy to active sunscreen ingredients is low, likely less than 1%.”

Patch Test Reactions Associated With Sunscreen Products and the Importance of Testing to an Expanded Series
By Erin Warshaw, et al.
Published July/August, 2013

“Of 23,908 patients patch tested, 219 (0.9%) had sunscreen coded as an allergen source…the most commonly affected areas were the face and exposed sites…The top 3 most frequent allergens in sunscreens were benzophenone-3 (70.2% for 10% concentration, 64.4% for 3% concentration), DL-alpha-tocopherol (4.8%), and fragrance mix I (4.0%).”

Here we find some of the allergens in the sunscreens weren’t the sunscreen chemicals, but fragrances and a form of Vitamin E.

Sunscreen Allergy: A Review of Epidemiology, Clinical Characteristics, and Responsible Allergens
By Erin Warshaw, Elyse Scheuer
Published March, 2006

“The prevalence of allergy in the general population to sunscreen agents is unknown. Among individuals referred for patch testing, the prevalence of allergy to active sunscreen ingredients is low, probably less than 1%.”

“2,715 patients referred for presumed photosensitivity disorders from 1983 to 1998. Sixty-two patients (2.3%) exhibited photoallergic reactions, and of these reactions, 65% were due to UV absorbers.”
The prevalence described here isn’t 2.3% or 65%. It’s 65% of 2.3%, that’s 1.5%.

Contact and Photocontact Sensitivity to Sunscreens: Review of a 15-year Experience and of the Literature
By Silvia Schauder, Hellmut Ippen
Published 1997

Looking at data from between 1981 to 1996, 402 patients with suspected clinical photosensitivity, 80 (20%) demonstrated a reaction to 1 or more UV absorbers.

What to keep in mind is that these are patients with suspected clinical photosensitivity and are not representative of a general population.

Some of the sunscreen chemicals used in this study, like para-aminobenzoic acid (PABA), isopropyl dibenzoylmethane, and Enzacamene, are no longer commonly found in sunscreens due to frequent skin reactions.

Allergies to sunscreen is a real occurrence, but it’s very likely not as prevalent as 25% of all people.

If you experience: burning, stinging, lasting redness, welts, hives, or any other signs of a reaction – you should consider discontinuing use of the sunscreen or skincare formula.

Consider testing new sunscreens or skincare on a small patch of skin before using them more liberally.

Medical care may be out of reach for many in the US, but a dermatologist or allergist can work with you to help pinpoint what ingredients are causing your reactions.

When is “Free From” just Fearmongering?

“Free from” claims need to be relevant to the formula to be, well relevant.

“Free from” claims are often attached to products and formulas that normally wouldn’t contain the ingredients. This is when “free form” marketing can turn into fearmongering.

Let’s look at story about KFC to understand why.

KFC or Kentucky Fried Chicken is a global fast-food chain that is famous for its fried chicken.

In 2012, KFC ran advertisements in Canada claiming that their chicken was “hormone free”.

Suddenly, some people worried. Were there hormones in other brands’ chickens? Was KFC healthier, safer, and “cleaner” because their chicken was hormone free?

The Canadian Food Inspection Agency, dedicated to the safeguarding of food, plants, and animals in Canada, responded:

‘Products cannot be labelled or advertised as “hormone free” as it may mislead consumers to believe that the meat in question does not contain any hormones…all meat, poultry and fish products contain naturally occurring hormones.’

What that statement says is that chickens naturally have hormones, so it can’t be “hormone free”.

KFC clarified that they meant that they served chicken “that’s raised without hormones.”

They meant they didn’t supplement their chickens with hormones, which implied that other brands did.

But since 1963 in Canada, you can’t give chickens hormones.

Turns out in reality all chickens in Canada are actually “raised without hormones.”

This happens a lot in skincare, in a few different ways.

Irrelevance: We’ll see products like facial oils say “Free from sodium lauryl sulfate”, when sodium lauryl sulfate is not a common or necessary ingredient in a facial oil formulation.

Too Broad: We’ll find claims like “Free from fragrance” claims on products where ingredients, like plant extracts impart a scent.

Inaccuracy: “Free from formaldehyde” claims are often attached to products that contain ingredients that release formaldehyde at safe levels to preserve the formula.

Undefined: “Cruelty free” is not a defined term. Some brands take it to mean they haven’t tested the product on animals. It might mean the finished product wasn’t tested, but the ingredients were. Or a contractor or authority did. Because it’s not a standard, it’s up to the brand to define it. Some organizations have created logos and definitions that brands use, but customers must verify the standards used and its claims.

“Free from” claims might have begun as a useful and quick declaration to potential customers and users.

“Free from alcohol” would be useful for a parent buying a mouthwash for their child.

“Free from animal-derived ingredients” would be useful for someone who is vegetarian or vegan.

Like almost any product messaging, “free form” statements have mostly turned into more real estate for advertising and marketing.

Often by implying a product is “free from” it implies it is superior and in today’s market “cleaner” than its competitors.

Ultimately this trend may end up being worse for the beauty and skincare community as they’re left anxious and confused.