Sunscreen Guide: SPF, PA Ratings and How Much to Use

6 min read · Updated 11 October 2026

If you only use one skincare product, dermatologists almost universally agree it should be sunscreen. It reduces sunburn, dark spots, premature wrinkles and the risk of skin cancer. Yet most people apply too little, choose a formula they dislike, and stop using it within weeks. This guide explains how to choose one you will actually wear.

UVA and UVB

Sunlight contains two types of ultraviolet light that reach the skin. UVB causes sunburn and is strongest around midday. UVA penetrates deeper, passes through clouds and window glass, and is the main driver of skin ageing and pigmentation. A good sunscreen needs to protect against both — labelled "broad spectrum".

What the numbers mean

SPF (Sun Protection Factor) measures protection against UVB. SPF 30 blocks about 97% of UVB; SPF 50 blocks about 98%. SPF 30 to 50 is enough for daily life.
PA ratings (PA+ to PA++++) measure protection against UVA, which matters most for pigmentation and melasma. Choose PA+++ or higher.
Water resistance (40 or 80 minutes) only tells you how long protection lasts while swimming or sweating.

Chemical, mineral or hybrid?

Chemical (organic) filters absorb UV light. They tend to be lightweight and invisible, which suits oily skin and darker skin tones. Mineral (physical) filters — zinc oxide and titanium dioxide — reflect and scatter light. They are gentle for sensitive skin but can leave a white cast. Hybrid sunscreens combine both. All are effective; the best sunscreen is the one you will wear every day.

For melasma and stubborn pigmentation, tinted sunscreens with iron oxides also block visible light, which can trigger pigment in deeper skin tones.

How much and how often

Most people apply a quarter to half of the amount used in laboratory testing, which dramatically lowers the real protection. Use the two-finger rule: squeeze sunscreen along the length of your index and middle finger for your face and neck.

Apply as the last step of your morning routine, about 15 minutes before going out.
Reapply every two to three hours outdoors, and after sweating, swimming or towelling.
Do not forget the ears, neck, back of the hands, and around the eyes.
Wear it indoors if you sit near windows — UVA passes through glass.
Makeup with SPF does not replace sunscreen; you would need a thick layer to get the labelled protection.

Making it work in hot, humid weather

In Indian summers and monsoon, heavy creams feel greasy and slide off with sweat. Gel, fluid or "aqua" textures with a matte finish are more comfortable for oily and combination skin. Sunscreen sticks and SPF sprays make midday reapplication over makeup easier. Combine sunscreen with shade, a hat and sunglasses during the strongest sun, usually between 10 am and 4 pm.

When to see a dermatologist

You get a rash, itching or burning every time you apply sunscreen — you may be reacting to a specific filter.
You notice a mole or spot that is new, changing or bleeding.
You burn very easily or take medicines that make you sun-sensitive.

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This guide is general educational information and is not a substitute for professional medical advice, diagnosis or treatment. See our medical disclaimer.