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What sunscreen is made of and how it works

What sunscreen is made of and how it works
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Sun on your skin is a surefire way to accelerate the visible signs of ageing, making sunscreen one of your greatest weapons. Choosing the right sort and applying it properly, however, aren’t always at the top of our list of summertime activities. It doesn’t help that we believe that all sunscreen is created equal.

Not applying sunscreen regularly enough or properly is a major issue, but there’s more: there is some evidence to suggest that some sunscreen ingredients can interrupt your hormones. This article introduces you to sunscreen in a deeper way, with a list at the end of suspect ingredients and those considered safe.

Read more about which sunscreen to choose in Sunscreen isn’t all it’s cracked up to be.

Why do we need sunscreen anyway?

UV rays come in two forms – UVA and UVB – and we need to protect ourselves from both kinds.

  • UVA is what causes us to tan (used in tanning beds)
  • UVB causes redness and sunburn (causes cancer)
  • Both damage the skin in different ways
  • ‘Broad spectrum’ on your sunscreen label means it protects you from UVA and UVB rays, which all sunscreens (over SPF 4) are required by Australian law to do.

How does sunscreen work?

Sunscreen is not magic and it’s useful to understand how it works so you can get the most out of it. Sunscreen has ingredients in it that ‘catch’ and absorb, or reflect and scatter the UV rays before it can get to your skin cells. Some ingredients are for UVA rays and some are for UVB, and in combination, they are broad spectrum.

Sunscreen ingredients

The active ingredient in sunscreen is one of two types: an organic chemical filter or inorganic metal oxide (the white zinc you can buy). Newer sunscreens may contain organic chemical particles that actually behave more like zincs.

  • Organic chemical filters: These filters absorb UV rays, and some reflect and scatter rays too.
  • Physical metal oxide blockers: reflect and scatter rays (like zinc – less popular due to ‘ghosting’ on skin, making it seem whiter, despite being more effective and safer)

Sunscreen sensitivities and allergic reactions

Dermatological irritation can occur with sunscreen use due to sensitivities or even allergies, so if you are sensitive or want to double check, it can pay to do a sensitivity test on your inner arm – if you have no adverse symptoms after a day, you’re good to go. Obviously this can be inconvenient or expensive, so check with family and friends and try before you buy, avoiding suspect ingredients where possible.

Most allergenic ingredients checklist:

  • Butyl methoxydibenzoylmethane
  • Oxybenzone
  • 4-methylbenzylidene camphor (4MBC) – Denmark has banned this from all products, USA and Japan have not approved it for use

Hormone disruptors

Some chemical sunscreens are suspected of being endocrine disruptors, which means they impact hormones via absorption through the skin. This is never good, but can be problematic in those who already have disrupted hormones, or are pregnant or breastfeeding. This impact is mostly theory and based on animal studies where high amounts of ingredient were used – we would never use that much as sunscreen, at least not in one day. It doesn’t mean it can’t have a cumulative effect.

Most common suspected endocrine disruptors:

  • Oxybenzone,
  • Octyl methoxycinnamate,
  • Homosalate and
  • 4-methylbenzylidene camphor (4-MBC) – Denmark has banned this from all products, USA and Japan have not approved it for use

Ingredients considered safe and effective:

  • Bemotrizinol (Tinosorb S or Escalol S)
  • Methylene bis-benzotriazolyl tetramethylbutylphenol (Tinosorb M or Bisoctrizole)

Tips and tricks for saving your skin in the sun and making the most of sunscreen

  • If you are going swimming at all, make sure you have a reliable water resistant sunscreen and reapply after being in the water – it does wash off.
  • If you are exercising, sweat pushes the sunscreen out of your pores and drips off your body. Wipe yourself down, then reapply sunscreen.
  • If you are in the sun, reapply your sunscreen every two hours religiously.
  • If you are applying sunscreen to babies, only apply to small areas if necessary, and use loose clothing and shade to protect your baby’s delicate skin as the first form of protection.
  • Sensitive skin and small children may do better with zinc-based metal oxide (physical blockers) sunscreens. It is more effective, less easy to wash off, and causes fewer sensitivity reactions.
  • Avoid sunscreen with insect repellent if possible – some insect repellents reduce the efficacy of sunscreens by significant percentages. Reapply more frequently.
  • Use enough 50+ sunscreen – between 7-9 teaspoons for an adult body.
  • Don’t rub it in too hard – it is absorbed into the top layer of skin.
  • Don’t forget your ears, neck, back of your hands, and tops of your feet or the bottoms of your feet if you are lying around.
  • Try to avoid relying heavily on sunscreen alone – dress with a lightweight, loose-fitting physical barrier and you will find yourself unscathed at the end of the day.

Got sun damage?
Talk to our expert dermatologists

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