Sunscreen: Why, Which, When, How?

Medical & Editorial Disclaimer. This guide is educational content, not individualized medical advice, diagnosis or treatment for any reader. It reflects a precautionary framework applied to publicly available regulatory and clinical-evidence literature. Statements about a filter's regulatory status or safety profile are made only where independently verifiable against a named source. This content does not replace individualized consultation with a dermatologist. Always verify the current ingredient list against the product label, since formulations change without notice.

As a dermatologist, I cannot emphasise enough how crucial sun protection is in maintaining healthy skin, preventing premature ageing, and reducing the risk of skin cancer. Sunscreens serve as a barrier against harmful UV radiation, which can lead to skin damage and accelerate the ageing process.

However, with numerous options available in the market, selecting the right sunscreen can be overwhelming. Let's break down the key aspects of sunscreen, including the types, SPF, protection from UVA and UVB rays, and the best choices for different skin types.

What Does Broad-Spectrum Mean?

Broad-spectrum sunscreen means a sunscreen that protects your skin from both main types of sun rays:

• UVA causes ageing, wrinkles and pigmentation

• UVB causes sunburn

But with modern lifestyles and screen time, skin is exposed to more than just direct sunlight. So today, true broad-spectrum protection should ideally cover the following.

UVA rays

• Go deep into the skin

• Cause early ageing, wrinkles, and dark spots

• Present all day, even on cloudy days and indoors, through windows

UVB rays

• Affect the top layer of skin

• Cause sunburn and redness

• Strongest during midday sun

Blue light

• Comes from phones, laptops, tablets, and LED lights

• May worsen pigmentation and dullness, especially in darker skin tones, though the evidence here is still developing rather than settled

• Iron oxides and the newer filter TriAsorB are the ingredients most consistently credited with reducing blue-light-related pigmentation. TriAsorB is currently the only sunscreen filter with a published clinical study specifically confirming reduced blue-light-induced skin damage, rather than a laboratory measurement alone.

Visible light

• Part of normal daylight, the part we can see

• Can trigger melasma and dark patches in melanin-rich skin, even without sunburn

• A combination of iron oxide and titanium dioxide is generally considered to offer better protection against this than either alone

Pollution protection

• Pollution particles settle on skin and contribute to free-radical damage

• This is associated with dull skin, breakouts, uneven tone, and faster visible ageing

• A sunscreen formulated with antioxidants and a film-forming base is generally considered to help reduce this additional burden, though this is a supporting benefit rather than a separately tested and rated coverage claim

What Is SPF and How Does It Work?

SPF (Sun Protection Factor) measures how well a sunscreen protects your skin from UVB rays, the main cause of sunburn and a documented contributor to skin cancer risk. When sunscreen is tested in laboratories, it is applied at 2 mg per cm² of skin, a thick, generous layer.

At this correct dose:

Then why do dermatologists recommend SPF 50?

Most people apply only 0.5 to 1 mg/cm², which is 25 to 50% of the tested amount. When less sunscreen is applied, real-world protection drops, and it drops faster than the SPF number alone would suggest.

Approximate real-world protection when under-applied:

This is the key reason SPF 50 is generally recommended: it provides a buffer against under-application, sweating, rubbing, and uneven spread, all of which happen in ordinary daily use.

What Is PA+++ Rating and How Does It Work?

PA rating tells you how well a sunscreen protects against UVA rays, the rays most responsible for tanning, pigmentation, wrinkles, and long-term skin damage.

Why PA+++ matters:

• UVA rays penetrate deeper than UVB

• They pass through glass, clouds, and windows

• They are a major contributor to pigmentation, melasma, and premature ageing

• UVA exposure is roughly constant through daylight hours, not concentrated around midday the way UVB is

PA rating is based on PPD (Persistent Pigment Darkening) testing, which measures how much UVA-induced tanning a sunscreen prevents. More plus signs mean higher UVA protection.

A PA+++ rating means the sunscreen reduces UVA-induced tanning by roughly 8 to 16 times compared with unprotected skin, based on the PPD test.

Types of Sunscreen

Physical Sunscreens (Mineral)

Common ingredients: Zinc Oxide, Titanium Dioxide

How they work. They sit on top of the skin and reflect and scatter UV rays, starting to work immediately after application.

Best for: sensitive skin, children, rosacea, eczema and post-procedure skin, pregnancy, and anyone prioritising a minimal-ingredient formula.

Pros: less irritation for most users, very stable in sunlight, and genuine broad UVA plus UVB protection.

Cons: can leave a white cast, especially on darker skin tones, and may feel heavier or thicker than a chemical formula.

Older-Generation Chemical Sunscreens

How they work. They absorb UV rays and convert them into heat, released from the skin. They typically need 15 to 20 minutes after application to start working.

Examples: Avobenzone, Octinoxate, Oxybenzone, Homosalate.

Why we recommend caution with this group specifically:

• These filters are generally less photostable than newer alternatives.

• Some users report eye irritation.

• FDA-sponsored pharmacokinetic studies have found several of these filters, oxybenzone and octinoxate among them, absorbed into the bloodstream at levels above the threshold the agency uses to decide whether further safety testing is warranted, after just a few days of regular use.

• Oxybenzone specifically has been detected in breast milk, urine, and placental tissue in population studies, confirming it crosses the placental barrier, and is flagged by regulatory and scientific reviews as a potential endocrine-active compound warranting continued study; the EU reduced its permitted concentration from 10% to 6% in 2022 on this basis.

• Because physical filters remain on the skin's surface rather than penetrating it or entering systemic circulation, Indian dermatologist consensus guidance recommends inorganic (physical) sunscreens with zinc oxide or titanium dioxide as the preferred choice in pregnancy, for children old enough to use sunscreen, and for anyone with reactive or sensitive skin.

New-Generation Chemical Filters

Modern sunscreens increasingly use newer filters that are generally more photostable and better tolerated than the older-generation group above.

Examples:

1. Tinosorb S (Bemotrizinol): strong UVA and UVB coverage

2. Tinosorb M (Bisoctrizole): covers UVA, UVB and partial visible light

3. Tinosorb A2B (Tris-Biphenyl Triazine): a micronized filter covering UVB and UVA2

4. Uvinul A Plus (DHHB): strong UVA protection

5. Uvinul T 150 (Ethylhexyl Triazone): one of the strongest UVB filters available

6. Mexoryl SX (Ecamsule): strong UVA protection

7. Mexoryl XL (Drometrizole Trisiloxane): broad UVA and UVB coverage, and helps stabilise other filters

8. Mexoryl 400 (MCE): currently the only filter specifically covering ultra-long UVA1, the 380 to 400 nanometre range

9. Iscotrizinol (DBT): a strong, photostable UVB filter

10. TriAsorB (Phenylene Bis-Diphenyltriazine): covers UVB, UVA and blue light up to 450 nanometres, the only filter in this list with a published clinical study confirming reduced blue-light-induced skin damage

Even these newer filters are not completely blocked by skin: independent research has found trace absorption for several of them too. What makes a modern filter a better choice is not that nothing gets in, but that the amount that does sits far below the level at which anything happens, together with a stronger overall stability and tolerability profile.

Quick comparison

How to Use Sunscreen: A Step-by-Step Guide

Step 1: Wash. Cleanse your face so sunscreen goes on to clean skin.

Step 2: Treat. Apply any treatment serums or actives you use.

Step 3: Moisturise, if your skin feels dry.

Step 4: Protect with a broad-spectrum sunscreen.

• Apply as the final step of your morning skincare routine, before make-up.

• Use about 1 to 2 teaspoons for the face and neck. This is more than most people use, and Indian dermatologist consensus guidance links under-application directly to the gap between a sunscreen's tested SPF and its real-world protection.

• Dot it on the forehead, cheeks, nose, and chin, then spread evenly.

• Cover all exposed areas, including the ears, jawline, and neck.

Step 5: Make-up (optional).

When to Use Sunscreen

• Every morning, as the final step of your skincare routine.

• Daily, even on cloudy days or indoors if sunlight enters the room, since UVA passes through glass and cloud cover.

• Year-round, regardless of season, since UV exposure is present in some amount every day.

• Apply before stepping out into sun exposure. For a water-resistant formula, allow 15 to 30 minutes for it to dry before swimming or heavy water exposure.

• Reapply after swimming, excessive sweating, or wiping your face. Indian dermatologist consensus guidance notes that with an adequately applied initial layer, reapplication may not be strictly necessary within an 8-hour period otherwise, though reapplying every 2 to 3 hours during active outdoor exposure remains a reasonable, simpler default for most people.

What to Pair Sunscreen With

• In general, sunscreen can be paired with most active ingredients, including vitamin C, niacinamide, hyaluronic acid, and azelaic acid.

• You can layer multiple SPF products, for example an SPF foundation over an SPF moisturiser over a base sunscreen, but SPF values do not add up linearly when layered this way, and layering multiple SPF products can increase the risk of the formula pilling on the skin.

• Avoid mixing sunscreen directly into moisturiser or foundation in your palm before application, since this dilutes the sunscreen and can reduce its effectiveness.

How to Choose the Best Sunscreen for Your Skin Type

Your skin type and concerns should guide your sunscreen selection. If you are unsure what suits you, our Sunscreen Finder Tool can help match a sunscreen to your skin type and concerns.

• For oily skin: opt for gel-based sunscreens with water as the first ingredient, and look for non-comedogenic formulas.

• For dry skin: choose cream-based sunscreens with hydrating ingredients like glycerin and ceramides.

• For sensitive skin: physical sunscreens with zinc oxide or titanium dioxide are generally the gentlest, well-tolerated option.

• For acne-prone skin: non-comedogenic, oil-free formulations are important; gel-based or water-based sunscreens are generally suitable choices to avoid contributing to breakouts.

Sunscreen for Kids

Under 6 months: direct sun exposure should be avoided altogether at this age, and Indian dermatologist consensus guidance does not recommend sunscreen use at all for infants this young. Shade, clothing, and timing outings around peak sun hours are the actual protection strategy here, not a sunscreen product.

6 months and older: a broad-spectrum sunscreen of SPF 15 or higher, applied before sun exposure and reapplied every 2 hours, is the general recommendation. Inorganic (physical) sunscreens with zinc oxide and titanium dioxide are specifically preferred for children, since chemical filters may contain potential allergens.

Our own review of the market uncovered something worth flagging: most sunscreens marketed as "kid-safe" in India actually use chemical UV filters, including some older filters with the safety questions discussed above. To check which sunscreen is genuinely suitable for a child, try our Safe Child Product Finder.

Conclusion

In today's skincare market, labels, ads, and influencer reels do not tell you the full story. What really matters is what is inside the bottle: the ingredients, their safety profile, and how they actually work on your skin.

That is where Dermatocare.com comes in. We look at what brands do not highlight and influencers do not mention, from outdated filters to marketing-driven formulations.

Before you buy your next skincare product, read the review on Dermatocare, because informed skin decisions come from science, not sponsorships.