SPF Properly Explained: What to Look For, How to Use It, and Why It Matters for Melasma
Journal Club · Dr Munroe Recommends
SPF, Properly Explained: What to Look For, How to Use It, and Why It Matters for Melasma
About Journal Club — Curated by Dr Munroe
Journal Club is where you'll find the most up-to-date references and findings, personally curated by Dr Munroe — a doctor and surgeon of nearly 15 years, with a Masters in Surgical Innovation and 10 years of aesthetics training. Every recommendation here is grounded in published evidence, clinical experience, and genuine client feedback.
Sunscreen is the single most effective anti-ageing product available, and also the one most people get slightly wrong - not through lack of effort, but because the label itself is confusing. Star ratings, SPF numbers, mineral versus chemical, tinted versus not. Below is a straightforward breakdown of what actually matters, how to use SPF properly through an ordinary day, and why pigmentation-prone skin - melasma in particular - needs an approach that a standard sunscreen doesn't provide.
Key Takeaways
- UVA and UVB do different jobs, and your SPF label tells you about both separately: UVA is the wavelength behind ageing and pigmentation, and its strength is shown by the UVA star rating (up to 5 stars); UVB is the wavelength behind burning, and its strength is shown by the SPF number.
- Face, hands and neck are treated as one continuous area of sun exposure - hands and neck are the most commonly missed, and show cumulative damage earliest. A foundation or moisturiser with SPF built in is better than no SPF at all, though it won't match a dedicated application.
- Sunscreen is reapplied, not just applied - every two hours during continuous exposure, and immediately after swimming, sweating or towel-drying. In practice: a top-up when you leave for lunch, on the way home from the office, or especially after a gym class.
- Shade, a hat and sunglasses are protection in their own right, not an optional extra - they don't wear off and don't need reapplying.
- Melasma is a common, chronic pigmentation condition driven by UV, visible light and hormonal factors. Tinted mineral sunscreen containing iron oxides is the one formulation shown to reduce relapse, because it's the only type that filters visible light as well as UV.
1. What to look for in an SPF, and why
Sunscreen labels carry two separate pieces of information, and it's worth understanding both rather than reaching for whichever bottle is nearest.
UVA is the wavelength that penetrates more deeply into the skin and is the main driver of photoageing and pigmentation. Its strength is shown by the UVA star rating - a UK-specific system, out of 5 stars, printed on the bottle.[1,2]
UVB is the wavelength responsible for sunburn, and its strength is shown by the SPF number itself. SPF 30 is the minimum I'd recommend for daily use; SPF 50 offers a meaningfully higher margin and is my general default for the face, and for anyone managing pigmentation.
Beyond those two numbers, a few other things are worth checking:
- Broad-spectrum on the label confirms the product protects against both UVA and UVB - this should be non-negotiable.
- Mineral filters (zinc oxide, titanium dioxide) tend to be better tolerated on sensitive skin, and are my general preference in the days after an in-clinic procedure.
- Tinted mineral formulas containing iron oxides add a layer of protection against visible light that plain sunscreen doesn't provide - more on why that matters in the melasma section below.
- Texture matters more than people expect. The best SPF is the one you'll actually wear every day, so a formulation that sits well under makeup and doesn't feel heavy is worth prioritising over a marginally higher star rating you won't use consistently.
2. Application: face, hands and neck
Sun exposure doesn't stop at the jawline. I treat the face, neck and hands as one continuous area - the backs of the hands, in particular, are one of the first places cumulative sun damage becomes visible, and they're consistently the area people forget.
A facial SPF (SPF 30-50, broad-spectrum) goes on every morning as the last step of a skincare routine, after moisturiser. The neck and the backs of the hands deserve a deliberate, separate application rather than an assumption that whatever's left on your fingers will cover them - a body or family SPF is a practical option for this.
SPF is its own step, not a property you borrow from another product. The order is: skincare (cleanser, serums, moisturiser), then SPF, then makeup on top once it's settled. If a foundation or moisturiser with SPF built in is genuinely the only sun protection going on that day, that's still better than nothing, but it isn't a substitute for that dedicated step - most of us apply far too thin a layer of makeup to rely on its SPF alone.
3. Reapplication
Sunscreen filters break down with time and UV exposure, so one morning application isn't enough to see you through a full day of meaningful sun exposure.
The standard guidance is to reapply every two hours during continuous outdoor exposure, and immediately after swimming, sweating or towel-drying.[2] In practice, that usually means a top-up when you step out for lunch, on the way home from the office, or especially after a gym class or anything that involves sweating.
The main barrier to reapplying isn't awareness, it's convenience - keeping a spray or stick SPF in your bag, car or desk drawer removes that barrier.
4. Beyond the bottle: shade, hats and sunglasses
Shade, a wide-brimmed hat and sunglasses are genuine protection, not a substitute for SPF - their advantage is that they don't degrade over the course of the day and don't rely on anyone remembering to reapply.
The skin around the eyes is thinner and more delicate than the rest of the face, and disproportionately vulnerable to UV. Sunglasses are one of the more meaningful, and most overlooked, protective steps you can take.
Ears, the back of the neck and the parting of the hair are commonly missed by SPF and shade alike, and worth a specific mention if you're prone to burning or pigmentation in those areas.
5. Travel and everyday exposure
Exposure isn't limited to obvious sun-holiday scenarios. Time spent driving, travelling or simply out and about counts as sun exposure - UVA passes through glass to a meaningful degree, even when it doesn't feel like being in direct sun, so SPF habits shouldn't switch off indoors or in transit.[3] A convertible with the roof down removes that barrier entirely, but the wider point holds for any car, train or office window: SPF is a daily habit tied to time spent outdoors and in transit generally, not a product reserved for beach days.
6. Melasma: what it is, and how SPF helps
Melasma is a common, chronic pigmentary condition that causes symmetrical brown or grey-brown patches, typically across the cheeks, forehead, upper lip and chin. It develops when melanocytes - the pigment-producing cells in skin - become overactive, and it's more common in women and in darker skin phototypes.[4]
Recognised triggers include UV exposure, visible light, heat, hormonal factors such as pregnancy or the contraceptive pill, and genetic predisposition. It tends to follow a relapsing-remitting course - it can improve significantly, then resurface with renewed exposure or hormonal change.[4]
This is where most sunscreen falls short. Standard sunscreen filters UV but not visible light, and visible light - particularly the blue-violet band around 415nm - is a separate, well-evidenced trigger for melasma. It can produce pigmentation that is more intense and longer-lasting than UV-induced pigmentation.[5]
Tinted mineral sunscreens containing iron oxides are the formulation shown to close that gap. A randomised trial published in the Journal of the American Academy of Dermatology found that adding iron oxide to a sunscreen reduced melasma relapse compared with the same formula without it;[6] a more recent randomised study reached the same conclusion over a full summer season.[7]
For anyone managing melasma, the practical takeaway is that broad-spectrum SPF is necessary but not sufficient. A tinted, iron-oxide-containing mineral formula is the meaningful upgrade - alongside consistent daily use and proper reapplication.
Managing melasma and not sure where to start? Book a skin consultation
7. Product picks, and why
These are the products I use myself and recommend most often:
If you're managing hyperpigmentation more broadly, ask about my Skincare Basics & Hyperpigmentation guide, which covers the full morning and evening routine and is available to clients in clinic.
Frequently asked questions
What should I look for on an SPF label?
Broad-spectrum protection, an SPF of 30-50, and a UVA star rating of 4-5 stars. The SPF number reflects UVB (burning) protection; the star rating reflects UVA (ageing) protection - you need both to be strong.
How often should I reapply sunscreen?
Every two hours during continuous outdoor exposure, and immediately after swimming, sweating or towelling dry. A practical rule of thumb is to top up whenever you're out for a meaningful length of time - lunch, the commute home, or after exercise.
What is melasma and what causes it?
Melasma is a common, chronic condition causing symmetrical brown or grey-brown patches on the face, driven by UV exposure, visible light, heat, hormonal factors and genetic predisposition. It tends to improve and then resurface with renewed exposure.
Why does tinted sunscreen help with melasma?
Standard sunscreen filters UV but not visible light, which is a separate trigger for melasma pigmentation. Tinted mineral sunscreens containing iron oxides filter visible light as well, and have been shown in randomised trials to reduce melasma relapse.
Is SPF 30 enough, or should I use SPF 50?
SPF 30 is the minimum recommended for daily use. SPF 50 offers a meaningfully higher margin of protection and is generally my default for the face, and for anyone managing pigmentation.
Do I need SPF if I'm mostly indoors or travelling by car?
Yes. UVA passes through glass to a meaningful degree, so time spent driving or near windows still counts as sun exposure, even without direct sunlight.
References
- NHS. Sunscreen and sun safety. nhs.uk
- British Association of Dermatologists. Sun Protection Fact Sheet. skinhealthinfo.org.uk
- Evaluation of UV-A and UV-B transmission through the windows of gas, hybrid, and electric vehicles. Arch Dermatol Res. 2024. PMC
- Melasma. StatPearls, NCBI Bookshelf. NCBI
- The emerging role of visible light in melanocyte biology and skin pigmentary disorders. J Clin Med. 2023. PMC
- Boukari F, Jourdan E, Fontas E, et al. Prevention of melasma relapses with sunscreen combining protection against UV and short wavelengths of visible light: a prospective randomized comparative trial. J Am Acad Dermatol. 2015;72(1):189-190.e1. PubMed
- Comparison of visible light-protective tinted sunscreen to untinted sunscreen to protect melasma patients during summer: a prospective randomized investigator-blinded study. PMC
Disclaimer: This guide is for general information only and does not constitute medical advice. Individual results and suitability may vary. If you have a diagnosed skin condition or are using prescription treatments, please consult your treating clinician before changing your skincare routine. For further information or to book a consultation, visit drmunroe.com or contact clinic@drmunroe.com.