SPF 50

SPF 50

Sunlight has two types of UV rays that reach your skin: UVA and UVB. They do different damage.
UVB is the shorter wavelength. It's the one that burns you. It hits the outer layer of skin, causes sunburn, tanning, and directly damages DNA in skin cells. It's the main driver of most skin cancers, including melanoma. UVB is stronger in the middle of the day and weaker in the morning and evening.
UVA is the longer wavelength. It doesn't burn, which is why people underrate it. But it penetrates much deeper, into the layer where collagen and elastin live. It's what ages your skin: wrinkles, sagging, loss of firmness, dark spots, and leathery texture over time. UVA also contributes to skin cancer risk. Unlike UVB, UVA is pretty constant all day long and passes through clouds and windows. If you sit by a window in an office, UVA is hitting you.
Sunscreens block these rays in one of two ways. Mineral filters (zinc oxide and titanium dioxide) are metal oxide particles that sit on top of your skin and reflect or absorb UV on the surface. They don't meaningfully enter your bloodstream. Chemical filters are small organic molecules that penetrate into the upper layers of skin, absorb UV, and convert it to heat. They do get absorbed systemically: the FDA has shown that filters like oxybenzone, avobenzone, and octocrylene show up in blood at measurable levels after a single day of normal use, and persist for days after.
For most modern chemical filters (Tinosorb, Mexoryl, Uvinul A Plus), systemic absorption hasn't shown clinical harm. For the older US chemical filters (oxybenzone, octinoxate, avobenzone, octocrylene), that's where the fertility and hormone concerns originate. If you're pregnant, trying to conceive, breastfeeding, or just risk-averse, mineral is the default safer choice. Otherwise, modern chemical filters are fine and cosmetically much nicer.
Flip the bottle over. Look at the active ingredients list.
Buy it if you see any of these:
  • Tinosorb S (bemotrizinol) or Tinosorb M (bisoctrizole)
  • Mexoryl SX, Mexoryl XL, or Mexoryl 400
  • Uvinul A Plus (diethylamino hydroxybenzoyl hexyl benzoate)
  • Uvinul T 150 (ethylhexyl triazone)
  • Zinc oxide at 10% or higher (ideally combined with titanium dioxide)
These are the modern filters. They cover UVA and UVB, stay stable in sunlight, and don't break down on your face over the course of a day.
Put it back if the active ingredients are only:
  • Avobenzone + octinoxate + octisalate + homosalate + octocrylene + oxybenzone
This is the standard US chemical sunscreen formula. It works for UVB (you won't burn), but UVA coverage is weaker and avobenzone degrades in sunlight. It's also the formula linked to the fertility concerns. If you're in the US and this is all you can find, go mineral (zinc oxide).
Also check:
  • SPF 50 or higher on the front
  • PA++++ (if it's an Asian sunscreen) or a UVA in a circle logo (European)
  • "Broad spectrum" is the bare minimum, not a guarantee of good UVA coverage
If the filters check out, the brand barely matters.

Specific bottles to grab

These use modern filters and are widely available globally. Bangkok stocks most of these in Watsons, Boots, EVEme, or online via Shopee/Lazada.
  • Beauty of Joseon Relief Sun: Rice + Probiotics SPF 50+ PA++++ (Korea) - consensus favourite. Cheap, light, no white cast.
  • Biore UV Aqua Rich Watery Essence SPF 50+ PA++++ (Japan) - watery gel, perfect for humid climates.
  • Anessa Perfect UV Sunscreen Skincare Milk SPF 50+ PA++++ (Japan) - sweat and water resistant, Asian beach standard, go-to for the beach or sports.
  • La Roche-Posay Anthelios UVMune 400 SPF 50+ (EU/global) - Mexoryl 400, technical gold standard.
  • ISDIN Fusion Water SPF 50 (Spain/global) - ultra-light, dries matte.
  • Ultra Violette Queen Screen SPF 50+ or Supreme Screen SPF 50+ (Australia) - Australian sunscreens are some of the most rigorously tested in the world.
US-only fallback: EltaMD UV Clear, Supergoop Mineral Play, or Vanicream Facial SPF (all zinc-based).

SPF 30 vs SPF 50

SPF 30 blocks roughly 97% of UVB. SPF 50 blocks about 98%. On paper, a rounding error. The real reason to default to SPF 50: almost nobody applies enough. Studies consistently find people apply about a quarter of the amount needed to hit the labelled rating, meaning your SPF 50 is performing closer to SPF 15 in practice. SPF 50 gives you a buffer. Higher than 50 is diminishing returns.

Notes

  • Ignore "SPF 100" marketing. Above 50 is diminishing returns.
  • Makeup with SPF. You'll never apply enough to hit the rating.
  • Most "natural" or "clean beauty" SPFs. Often max out at SPF 30 with poor UVA coverage.
  • "You need sun for vitamin D so skip sunscreen." Incidental exposure on hands, arms, and legs during normal life gives you plenty. Supplement D3 if low.
  • Expired sunscreen. Filters degrade. Replace every 1-2 years.

One note for women

SPF ratings work the same regardless of sex. What differs: oestrogen drives melasma, the blotchy hyperpigmentation that's much more common in women, especially during pregnancy or on hormonal birth control. If you're prone to melasma, you need a sunscreen that also blocks visible light, which means a tinted mineral SPF with iron oxides. Untinted sunscreens, even great ones, don't block visible light and won't prevent melasma flare-ups.
Sunscreens are regulated as OTC cosmetics or drugs depending on region and are widely available without prescription.