Quick Answer
SPF measures UVB. PA measures UVA. Neither measures visible light — and on Indian skin, visible light drives pigmentation that no SPF number accounts for.
For tropical conditions: SPF 50, PA++++, applied properly. How much you use matters more than the number on the bottle — most people apply a fraction of the tested amount.
And if pigmentation is your concern, a tinted formula covers what a clear one can't.
The essentials
- UVA is about 95% of the UV reaching you, is constant year-round, and passes through cloud and glass.
- UVB peaks midday and causes burning. SPF measures this one only.
- Visible light pigments deeper skin — and no rating on the bottle covers it.
- Metal oxides absorb UV; they don't work like a mirror.
- Melanin is worth roughly SPF 3–4 — real, and nowhere near enough.
- Most people under-apply, which costs more protection than choosing a lower SPF would.
- Reapply every two hours outdoors, sooner with sweat or swimming.
In this article
UVA And UVB — What Each Does
UVB (280–320nm) is the burning wavelength. It's most intense in the middle of the day, varies with season, and is largely blocked by glass. It's what SPF measures.
UVA (320–400nm) penetrates deeper into the skin, driving photoaging, collagen breakdown and pigmentation. It makes up roughly 95% of the UV that reaches you, stays relatively constant through the day and across seasons, and passes through cloud and window glass.
Why this matters more here than in temperate guidance. UVA is the wavelength most implicated in pigmentation, and it doesn't take a sunny day or an outdoor afternoon to reach you. A high SPF with poor UVA coverage leaves the pigmentation problem largely untouched — which is why the PA rating deserves as much attention as the SPF number.
Visible Light: The Gap In Every SPF Number
This is the part almost no sunscreen guidance covers, and for Indian skin it may be the most consequential thing on this page.
Neither SPF nor PA measures it
Research on melanocompetent skin has shown that visible light — ordinary light you can see — induces pigmentation in darker skin types, producing darkening that is more persistent than that caused by UVA at comparable doses. In lighter skin, the same exposure does considerably less.
SPF describes UVB. PA describes UVA. Visible light is measured by neither — so a sunscreen with excellent ratings on both can leave this entirely uncovered. And unlike UVB, visible light passes through window glass without obstruction.
What blocks it is iron oxides — the pigments that tint a sunscreen. Which means that on medium-to-deep skin, a tinted formula isn't a cosmetic preference. It closes a gap the label never mentions.
This explains a frustration a lot of people describe: wearing sunscreen diligently and still seeing pigmentation return. If the formula is clear, part of the relevant exposure was never being covered.
SPF, PA And What They Actually Tell You
SPF is usually described as a blocked percentage, and that framing misleads. SPF 30 blocks about 97% of UVB, SPF 50 about 98% — which sounds like a rounding error.
Read it as transmitted dose instead
SPF 30 lets through about 3% of UVB. SPF 50 lets through about 2%. Stated that way, SPF 50 transmits roughly a third less UV than SPF 30 — which is a real difference, not a rounding error.
Combine that with near-universal under-application, and the headroom matters. For Indian conditions, SPF 50 is the sensible default, and the "30 is basically the same" argument doesn't survive the arithmetic.
PA is the UVA scale, used across Asian markets: PA+ through PA++++. Given that UVA is most of the UV reaching you and drives pigmentation, PA++++ is worth prioritising here — arguably more than pushing SPF beyond 50.
"Broad-spectrum" means both are covered. A high SPF alone tells you about burning, not about ageing or pigmentation.
How Filters Work
A correction worth making
Mineral filters are almost universally described as working like a mirror, reflecting UV away. That isn't what happens. Zinc oxide and titanium dioxide absorb the large majority of the UV they intercept — around 95% — and scatter only a small fraction.
Which means the "physical versus chemical" split is largely a marketing distinction rather than a mechanistic one. Both families mostly do the same thing. What actually differs is texture, finish, photostability and how the formula sits on your skin.
| Feature | Organic filters | Metal oxides |
|---|---|---|
| Mechanism | Absorb UV | Also absorb, plus a small amount of scattering |
| Feel | Lighter, invisible | Heavier; white cast unless tinted or micronised |
| On deeper skin | No cast | Tinted versions solve the cast and add visible-light cover |
| Photostability | Varies by filter; modern ones are stable | Stable |
| In humidity | Usually more wearable | Can feel heavy |
Choose on how it feels, not on which family it belongs to. The sunscreen you'll actually wear every day outperforms the theoretically superior one you won't.
Sunscreen And Deeper Skin Tones
Melanin provides real protection — worth roughly SPF 3 to 4. That's genuine, and nowhere near sufficient. It's the difference between burning less easily and being protected.
And the relevant harms differ. On deeper skin the dominant concerns are pigmentation, melasma and photoageing rather than burning — and melanin offers least protection against exactly the wavelengths that drive them, since it's weighted toward UVB rather than UVA, and does nothing about visible light.
The white cast problem is a protection problem
A sunscreen that leaves a grey cast doesn't get worn, and an unworn sunscreen protects nobody. This isn't vanity — it's adherence, and adherence is the whole game. Tinted mineral formulas solve the cast and add iron oxides for visible light, which makes them the strongest option here rather than a compromise.
The Part That Decides Everything: How Much
SPF is measured at 2mg per square centimetre — roughly half a teaspoon for the face and neck, or two finger-lengths of product. Most people apply between a quarter and half of that.
Protection doesn't fall proportionally with quantity — it falls faster. Which means an SPF 50 applied thinly can deliver considerably less than the label suggests, and your application habit affects your real protection more than the number you bought.
- Two finger-lengths for face and neck. It will feel like too much. It isn't.
- Every two hours outdoors, and sooner after sweating, swimming or towelling.
- Don't miss ears, the back of the neck, the hairline, and the backs of hands while driving.
- Indoors near a window still counts — UVA and visible light both pass through glass.
Choosing For Indian Conditions
Baseline: SPF 50, PA++++, worn daily. In humidity, texture decides whether it gets worn at all — gel and fluid formats generally survive Indian summers better than creams.
If pigmentation or melasma is your concern: a tinted formula, for the visible-light reason above. This is the single highest-value change most people can make.
If you're oily or break out: lightweight fluid or gel textures, and treat "non-comedogenic" as a hint rather than a guarantee — it's an unregulated term. Your own skin over three or four weeks is the real test.
If your skin is dry or reactive: fragrance-free, and a formula with humectants or ceramides built in.
Myths
"Dark skin doesn't need sunscreen"
Melanin gives roughly SPF 3–4 — real, and not enough. And the concerns that matter most on deeper skin are pigmentation, melasma and photoageing rather than burning, which is exactly where melanin protects least. Visible light, which melanin doesn't address at all, drives pigmentation specifically in darker skin types.
"SPF 100 is twice SPF 50"
No — SPF 50 transmits about 2% of UVB and SPF 100 about 1%. Real, but small, and well behind application quantity in importance. Going from SPF 30 to 50 is the meaningful step; beyond that, apply more of what you have.
"Only on sunny days"
UVA passes through cloud with little reduction, and it's most of the UV reaching you. Overcast in monsoon season still delivers meaningful exposure — and since UVA is the pigmentation wavelength, cloudy-day gaps add up precisely where you'd notice.
"SPF in my makeup is enough"
Almost never, because nobody applies foundation at 2mg per square centimetre. SPF in cosmetics is a useful supplement to a proper sunscreen underneath, not a replacement for one.
"Sunscreen will make me vitamin D deficient"
Reviews of the evidence don't support this for typical everyday use — incidental exposure and diet both contribute. If you have reason to be concerned about your vitamin D status, that's a blood test and a conversation with your doctor, not a reason to skip sun protection.
Questions, Answered
Why does my pigmentation come back even though I wear sunscreen?
Possibly because of visible light. It drives pigmentation in darker skin types, more persistently than UVA at comparable doses — and neither SPF nor PA measures it, so a clear sunscreen with excellent ratings can leave it uncovered. Iron oxides in tinted formulas are what address it. Application quantity is the other common answer: most people use well under the tested amount.
What SPF should I use in India?
SPF 50 with PA++++. Read as transmitted dose rather than blocked percentage, SPF 50 lets through about 2% of UVB against SPF 30's 3% — roughly a third less — and combined with typical under-application, that headroom is worth having. Prioritise the PA rating too, since UVA is most of what reaches you and drives pigmentation.
Do mineral sunscreens reflect UV away?
Mostly no, despite how universally that's repeated. Zinc oxide and titanium dioxide absorb around 95% of the UV they intercept and scatter only a small fraction — the same broad mechanism as organic filters. "Physical versus chemical" is largely a marketing distinction. Choose on texture, finish and whether you'll wear it daily.
How much should I apply?
About two finger-lengths for face and neck — roughly half a teaspoon, which is the amount SPF is tested at. Most people use a quarter to a half of that, and protection falls faster than the quantity does. Your application habit affects real protection more than the number on the bottle.
Do I need it indoors?
Near a window, yes — UVA passes through glass, and visible light passes through completely. Deep inside a room away from windows it matters far less. If you're managing melasma or pigmentation and sit by a window for hours, it's worth wearing.
Does sunscreen make brightening products work better?
It's closer to a prerequisite than an enhancement. UV restimulates the pigment pathway that brightening actives are trying to slow, so without daily protection you're working against yourself. If you use tranexamic acid, niacinamide or alpha-arbutin without sunscreen, you're getting a fraction of what the routine could do.
The Bottom Line
SPF 50, PA++++, two finger-lengths, every day — and reapplied when you're out. If pigmentation is your concern, make it tinted, because visible light is the exposure no number on the bottle accounts for. And melanin is worth about SPF 3 — genuine protection, and not remotely enough on its own.
References
- Rai R, Shanmuga Sekar C, Srinivas CR. Photoprotection. Indian Journal of Dermatology, Venereology and Leprology. 2012;78(5):599–606.
- Mahmoud BH, Ruvolo E, Hexsel CL, et al. Impact of long-wavelength UVA and visible light on melanocompetent skin. Journal of Investigative Dermatology. 2010;130(8):2092–2097.
- Passeron T, Lim HW, Goh CL, et al. Photoprotection according to skin phototype and dermatoses. Journal of the European Academy of Dermatology and Venereology. 2021;35(7):1460–1469.
- Cole C, Shyr T, Ou-Yang H. Metal oxide sunscreens protect skin by absorption, not by reflection or scattering. Photodermatology, Photoimmunology & Photomedicine. 2016;32(1):5–10.
- Faurschou A, Wulf HC. The relation between sun protection factor and amount of sunscreen applied in vivo. British Journal of Dermatology. 2007;156(4):716–719.
- Diffey BL. When should sunscreen be reapplied? Journal of the American Academy of Dermatology. 2001;45(6):882–885.
- Kullavanijaya P, Lim HW. Photoprotection. Journal of the American Academy of Dermatology. 2005;52(6):937–958.
- Battie C, Jitsukawa S, Bernerd F, et al. New insights in photoaging, UVA induced damage and skin types. Experimental Dermatology. 2014;23(Suppl 1):7–12.
- Passeron T, Bouillon R, Callender V, et al. Sunscreen photoprotection and vitamin D status. British Journal of Dermatology. 2019;181(5):916–931.
- Grimes PE. Management of hyperpigmentation in darker racial ethnic groups. Seminars in Cutaneous Medicine and Surgery. 2007;26(3):195–203.
Note to editor — this article has the best reference list in the batch, and the writing was working against it. Fifteen of the sixteen original entries are real, on-topic photoprotection papers — Diffey on reapplication, Faurschou on application quantity, Passeron on vitamin D, Rai in the Indian Journal of Dermatology, Venereology and Leprology. After five articles with inflated reference badges, this one nearly earns its claim; the only entry that isn't a study is Lim & Draelos, which is a textbook. Most have been retained. 🔴 The dominant problem was hedging. "Published research indicates", "published evidence suggests" and "published studies have documented" appeared over sixty times, opening nearly every sentence. That costs three ways: it's exhausting to read, it makes well-supported claims sound tentative — UVA penetrates glass is established physics, not something evidence merely suggests — and it works against AI retrieval specifically, since a model extracting an answer has to strip the hedge to reach the claim, and hedged text gets summarised less confidently. Confidence now tracks the evidence: settled physics is stated plainly, genuinely uncertain items are still qualified, and the distinction now carries meaning. 🔴 The mineral filter mechanism was wrong. The table gave "reflection + scattering" — metal oxides absorb around 95% of the UV they intercept and scatter only a small fraction. This contradicted two other pages in your library (zinc oxide and sunscreen selection), both of which state it correctly. Corrected, with Cole added as the reference. ⚠️ Visible light appeared once, in passing, in section 08. This is the SPF hub — the page five other articles should point at — and visible light is the most important gap for Indian skin, since neither SPF nor PA measures it. It now has its own section, so the hub owns the point. SPF framing has been aligned with the sunscreen-selection article: transmitted dose rather than blocked percentage. 🔴 Two internal links were relative (melasma, hyperpigmentation) with no domain while others were absolute; removed pending the canonical path decision. 🔴 Standing blocker: five articles now carry the visible-light section and should all link here — the hub URL is still unresolved across the library.
