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Why do I have to wait for sunscreen to work? Episode 19

For the first time ANYWHERE – we explain WHY you have to apply sunscreen 30 minutes before you go outside. Even better, we reveal two time saving sunscreen secrets.   All this and and a new edition of Beauty Science News!    We really should start charging for this stuff. 

Show notes

Beauty Science News: New anti aging antioxidant

Here’s a story that’s getting a lot of press – a new anti-aging anti-oxidant called Tiron.

News Headlines about Tiron: 

  • MedicalDaily.com: Antioxidant Tiron Is An Anti-Aging Skin Miracle
  • HuffPo: Antioxidant Tiron… ‘Protects Against Sun Damage And May Prevent Premature Ageing’
  • DailyMail: The molecule that holds key to younger looking skin
  • ScienceDaily: Fresh faced: Looking younger for longer

What is Tiron and does it live up to the hype?  Work done at Newcastel University, funded by Unilever, found that 4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate, was THE best at stopping UVA damage to mitochondria, which are the energy making parts of our cells.

Testing and results. They treated skin cells treated with a range of antioxidants and then exposed them to UVA radiation and measure the cells for DNA damage.

  • Tiron: 100% protection against mitochondrial DNA damage.
  • Resveratrol: 22% protection of both UVA and stress-induced damage.
  • Curcumin: 16% protection against oxidative stress and 8% against UVA.

So what does this mean? The researchers want to use this information to develop/identify other materials that are have safe to use on humans. Because “Tiron is not a naturally occurring compound and has not yet been tested for toxicity in humans although there have been a few studies on rats.“

The trouble with Tiron. Surprisingly, there was no mention of why the researchers wouldn’t do the toxicity testing on Tiron first of all. Second of all, what makes them think this product will do anything when applied topically to skin or when metabolized after ingestion. Looks like a good first step but it’s FAR from being the next anti-aging miracle.

Question of the week: Why do I have to wait 30 mins for sunscreen?

Shannon asks…I’ve read in many places that you have to put on sunscreen 30 minutes before going outside. Why is that? Why doesn’t the sunscreen start to work as soon as you put it on? Does something happen in that half an hour that makes it work differently?

(You can find Shannon at http://www.agirlsgottaspa.com)

Sunscreens have different forms but all must coat skin with a layer of UV absorber

Emulsions: individual particles suspended in oil/water mixture

Pros & cons: The most versatile and most aesthetically pleasing because of good application spreading properties and non-greasy feel. Also very efficacious because deliver a thicker layer which tends to be less transparent to light. Also, affordable because because water makes them cheaper. Have stability problems, active ingredient can settle out,  emulsions can become contaminated by micor-organisms due to presence of water.

Oils: Dissolved in a spreadable form

Pros & cons: Great spreadability and are also easy to formulate with. More stable than emulsions, fewer micro issues since no water.  Can be less effective because they deliver a thinner, more transparent layer. More expensive. Also, oils are solvents that can interfere with the UV absorption ability.

Sticks: Dissolved in a waxy form

Pros & cons: Excellent for touchup on nose or face. Have a wax base which it usually the most waterproof. Difficult to apply over large ares so not practical for use over the entire body. Wax base tends to give greasiest feel.

Powders: individual particles dispersed with other solids

Pros & cons: Good for two-in-products like makeup with sunscreen. A good way to provide a little SFP touch up. They don’t set up a uniform film so they are not as effective. Typically applied to all areas of the face so they’re not a good stand alone product.

Reason to wait #1: Sunscreens don’t form a film instantly

More precisely, time for film formation on skin varies with delivery form

  • Emulsions take the longest to form films because particles must coalesce but they are most effective.
  • Solutions are faster but a little less effective
  • Sticks and powders are fastest but provide the poorest coverage.

Reason to wait #2: Water proofing takes time

The ingredients used to make the product water resistant take time to dry and form a water proof film.  The sooner you go in the water after applying sunscreen, the more sunscreen will rinse away.

Two time saving sunscreen “hacks”

  • If you forget to apply sunscreen before going outside: use an oil based product
  • If you want “instant” protection before going in the water: use a stick

The bottom line

There is a sound, scientific reason for applying sunscreen 30 minutes before going out side. But by understanding the difference between product forms you can have the best chance at getting the coverage that you need.  And you can even know which forms are best to use when you forget to apply product in advance.


Study on the occlusivity of oil films Hisao Tsutsumi , Toshiaki Utsugi , Shizuo Hayashi 1979 JSCC.

Sunscreens: Development: Evaluation, and Regulatory Aspects.

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Buy your copy of It’s OK to Have Lead in Your Lipstick to learn more about:

  • Clever lies that the beauty companies tell you.
  • The straight scoop of which beauty myths are true and which are just urban legends.
  • Which ingredients are really scary and which ones are just scaremongering by the media to incite an irrational fear of chemicals.
  • How to tell the difference between the products that are really green and the ones that are just trying to get more of your hard earned money by labeling them “natural” or “organic.

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Comments on this entry are closed.

  • Beke Beau February 25, 2014, 6:44 am

    But wait! What about mineral sunblocks, e.g. zinc oxide and titanium dioxide?

    • Randy Schueller February 25, 2014, 8:31 am

      That’s a great question! Theoretically they should start working right away since they’re based on solid particles. Then again, it’s possible that the particles “settle into place” once their on your skin to form a uniform film. I’ve never seen any data on this. But if it is true, then that’s the best time saving hint of all – just use a mineral sunscreen and you could go out in the sun right away!

  • Nicole February 25, 2014, 9:08 pm

    How long are each effective? If I put on sunscreen under my makeup, how long am I good for?

    • Randy Schueller February 26, 2014, 11:06 am

      Nicole: You should reapply sunscreen every couple of hours if you’re getting a lot of exposure. That’s because the UV absorbers get “used up” over time.

      • Charlotte April 23, 2015, 11:21 pm

        Hi Randy

        Do I have 2 hours protection from UV rays from the moment I put the sunscreen on or after 2 hours exposed to sunlight? For example I put my sunblock on 30 minutes before leaving for work (a 30 min walk) and then I pop out on my lunch hour a few hours later for 20 mins. Will I still be protected?

        • Randy Schueller April 24, 2015, 7:12 am

          It may not make a huge difference (depending on how much sunlight you’re exposed to while you’re at work) but to get the maximum protection you should reapply every 2 hours. (Or at least before going back out in the sun.)

  • A Girl's Gotta Spa! February 25, 2014, 9:15 pm

    Thanks for featuring and answering my question!

  • rozy February 26, 2014, 9:24 pm

    Finds miracle antioxidant.
    Decides not to do toxicity studies.

    Claim to be scientists.
    Subscribes to naturalistic fallacy.


  • rozy February 26, 2014, 9:51 pm

    So hard to find any sunscreens with just zinc in Canada! Actually I have never found one. I don’t like how titanium makes me white and doesn’t work as well. Maybe I should start my own zinc sunscreen brand (with parabens)!

  • Radiance Hair and Beauty February 27, 2014, 3:05 am

    How we used the Beauty Brains Show episode 19 with our work ????

  • Kerry Prendergast February 27, 2014, 10:56 pm

    The instructions on all of the sunscreens I have state to wait 15 minutes. Where does the 30 minutes come from?

    • Randy Schueller February 28, 2014, 7:35 am

      @Kerry: Different sources quote different waiting times. For example, the American Melanoma Foundation says 30 minutes. But whether it’s 15 or 30 the important point is that there’s a “waiting period.”

  • www.radio-gielda.pl May 19, 2014, 11:16 am

    Thanks for finally writing about >Why do I have to wait for sunscreen to work?

    The Beauty Brains Show episode 19 <Loved it!

  • Aloha!! May 30, 2014, 1:49 am

    I’ve read somewhere that our unprotected skin starts get sunburn if we go outside for more than 15 or 20 minutes. Is that mean our nature skin can protect itself from the sun for approximately 15 minutes? So, do we really have to wait after wearing sunscreen? I meant that it usually takes a couple minutes to go out, then our skin will fight for itself for 15 minutes and by that time, our sunscreen starts working. Am I right?

    • Randy Schueller May 30, 2014, 7:28 am

      If unprotected skin starts to get sunburn after 15 or 20 minutes it’s because it has absorbed UV rays for that amount of time. If you apply sunscreen before going out your skin won’t absorb all that radiation.

  • Samantha April 9, 2016, 4:31 pm

    What about sunscreen setting face sprays like the supergoop spf 50? I find it’s the easiest to use and the most lightweight, but does the 30 minute wait time still apply?

    • Randy Schueller April 10, 2016, 12:46 pm

      If you’re talking about their lip product then I’d say yes because it uses the same type of standard organic UV absorbers.

      Active ingredients: Avobenzone 3% Homosalate 10% Octinoxate 7.5% Octisalate 5%

      Inactive ingredients: Hydrogenated Polyisobutene, Butyloctyl Salicylate ,Polyester-7,Diisopropyl Sebacate, Isodecyl Neopentanoate, Lauryl Lactate, Neopentyl Glycol Diheptanoate, Polyester-8, Tribehenin, Phenoxyethanol, Trihydroxystearin, Menthone Glycerin Acetal, Diethylhexyl Syringylidenemalonate, Polybutene, Tocopheryl Acetate, Polysilicone-15, Octyldodecanol, Elaeis Guineensis (Palm) Oil, Benzoic Acid, Tocotrienols, Helianthus Annuus (Sunflower) Seed Oil, Dehydroacetic Acid, Tocopherol, Caprylic/Capric Triglyceride, BHT, Vitis Vinifera (Grape) Seed Extract, Laminaria Ochroleuca Extract