What is the difference between UVA and UVB rays?

The sun does more than give you warmth

The sun is the closest star to Earth. It gives us light, warmth, and energy. But sunlight is not just the bright light you see. It also carries invisible rays that your eyes cannot detect and your skin cannot feel in the moment. Two of those invisible rays, UVA and UVB, reach the surface of the Earth every single day and interact with your skin whether you notice them or not.

Understanding the difference between UVA and UVB is not just a science lesson. It is practical knowledge that helps you make better choices about sun protection for yourself and your family.

This article explains both types of rays from the ground up, in simple language, with everything you need to know to understand sunscreen labels, choose the right product, and build a habit of daily protection.

What is ultraviolet light?

Light is more than what we can see

When you look at sunlight through a prism, it splits into the colours of a rainbow: red, orange, yellow, green, blue, indigo, and violet. These are the wavelengths of visible light, the part of sunlight that human eyes can detect.

But sunlight contains more than visible light. Beyond the violet end of the rainbow, there are wavelengths that are shorter and carry more energy. These are called ultraviolet (UV) rays. The word "ultraviolet" comes from Latin and means "beyond violet."

UV rays are invisible. You cannot see them. You cannot feel them as heat the way you feel infrared radiation. But they interact with the cells of your skin on a molecular level.

The electromagnetic spectrum

All light travels in waves. The distance from one wave peak to the next is called wavelength, measured in nanometres (nm). One nanometre is one billionth of a metre.

The electromagnetic spectrum arranges all types of radiation by wavelength:

UV radiation is divided into three bands:

UVC is the most powerful of the three, but the Earth's ozone layer absorbs it completely before it reaches us. UVA and UVB are the ones we need to understand and protect against.

UVB rays explained

What are UVB rays?

UVB stands for Ultraviolet B. These rays have a shorter wavelength than UVA, which means they carry more energy per wave. They are the more energetic of the two types that reach your skin.

UVB rays are partially filtered by the atmosphere, but enough of them reach the Earth's surface to have a significant effect on your skin.

What do UVB rays do?

UVB rays are absorbed mostly by the outer layer of your skin, called the epidermis. When UVB rays hit the skin cells in this layer, they directly damage the DNA inside those cells. This damage triggers an immune response in your body, which is what causes sunburn.

Sunburn is not caused by heat. It is caused by UV radiation damaging the DNA in your skin cells. The redness, tenderness, and peeling you see are your immune system's response to that damage.

UVB rays are also the primary driver of the skin producing Vitamin D. When UVB hits the skin, it converts a compound in the skin into Vitamin D3, which is then processed by the liver and kidneys into the active form of Vitamin D your body uses.

When are UVB rays strongest?

UVB intensity varies based on several factors:

In India, UVB intensity is high for most of the year due to the country's proximity to the equator. In cities like Chennai, which is close to the equator, UVB radiation is significant throughout the year, not just in peak summer.

Does UVB go through glass?

Standard glass blocks most UVB rays. This is why you typically do not get sunburned while sitting inside a car with the windows up.

However, UV-blocking depends on the type of glass. Windshields are often laminated and block most UV. Side and rear windows in older cars may offer less protection.

UVA rays explained

What are UVA rays?

UVA stands for Ultraviolet A. These rays have a longer wavelength than UVB, which means they carry less energy per wave. However, that longer wavelength allows them to penetrate deeper into the skin.

UVA rays make up about 95% of all UV radiation that reaches the Earth's surface. They are present throughout the day, not just during peak hours. They are present throughout the year, not just in summer. And they pass through clouds and glass with very little reduction.

What do UVA rays do?

Unlike UVB, which is absorbed by the outer skin layer, UVA rays penetrate into the dermis, the deeper layer of skin beneath the epidermis. In the dermis, your skin stores collagen and elastin, the proteins that keep skin firm and elastic.

UVA rays cause damage in two ways. First, they generate free radicals, unstable molecules that damage the DNA, proteins, and fats in skin cells. This is called oxidative damage. Second, UVA rays directly damage the DNA in deeper skin cells, though this mechanism is less direct than UVB.

The effects of UVA damage tend to be cumulative and long-term. They include premature skin ageing, loss of skin firmness, uneven skin tone, and increased risk of skin cancer over years and decades of exposure.

UVA rays also cause tanning. When UVA hits the skin, it triggers melanocytes (the cells that produce pigment) to release and darken existing melanin. This is why you tan after sun exposure. A tan is not a sign of health. It is a sign that your skin has been damaged and is trying to protect itself by producing more pigment.

When are UVA rays present?

This is what makes UVA rays more insidious than UVB. You can feel a sunburn. You cannot feel UVA damage happening. It accumulates quietly over years.

UVA vs UVB side by side

Reading sunscreen labels — SPF and PA ratings

Buying sunscreen is only useful if you can understand what the label is telling you. Here is how to decode the two most important ratings.

What is SPF?

SPF stands for Sun Protection Factor. It measures how well a sunscreen protects against UVB rays specifically.

SPF is expressed as a number: SPF 15, SPF 30, SPF 50, SPF 50+.

Here is what the number means. Without sunscreen, if it takes your skin 10 minutes to start showing a reaction to UVB exposure, then SPF 50 theoretically extends that time by a factor of 50, to 500 minutes. But in practice, SPF ratings are best understood as percentages of UVB blocked.

The difference between SPF 30 and SPF 50 may look small in percentage terms, but it represents a meaningful reduction in UV dose reaching your skin, especially with daily and cumulative exposure over months and years.

Important to remember: SPF only tells you about UVB protection. It says nothing about UVA protection. This is why the PA rating exists.

What is the PA rating?

PA stands for Protection Grade of UVA. It is a rating system developed in Japan and widely adopted across Asia, including India.

PA is expressed with plus signs: PA+, PA++, PA+++, PA++++.

Each additional plus sign represents a doubling or more of UVA protection. PA++++ is the highest grade available and represents the most robust UVA defence.

Reading a label: what to look for

When you pick up a sunscreen in India, here is how to read the label quickly:

1. Look for SPF 50 or above for adequate UVB protection
2. Look for PA++++ for the highest available UVA protection
3. Check that it says "broad spectrum," which means it covers both UVA and UVB
4. Check the UV filters listed in the ingredient list: these are the active ingredients doing the protecting

Common UV filter names you may see on labels:

A sunscreen with SPF 50 PA++++ gives you both strong UVB protection and the highest rated UVA protection. This combination is what makes a sunscreen genuinely broad spectrum.

East24 sunscreen and how it addresses UVA and UVB

East24 is India's everyday family sunscreen brand. Both products, Power Protect SPF 50 PA++++ and Super Hydrating SPF 50 PA++++, are formulated to provide broad spectrum protection against both UVA and UVB rays.

UV filters used in East24 formulations

East24 uses a combination of three proven UV filters:

This three-filter combination covers the full UV spectrum and works together to deliver SPF 50 PA++++ protection in both variants.

Power Protect SPF 50 PA++++

Power Protect is formulated without silicone emollients. It uses a polymer network as the base, which gives it a non-greasy finish and makes it suitable for everyday wear, including for people who prefer a lightweight texture. It is suited for adults and older children who are active outdoors and need protection that sits comfortably under clothing or on exposed skin.

Super Hydrating SPF 50 PA++++

Super Hydrating uses Cyclopentasiloxane and Dimethiconol as emollients, which give it a smooth, glide-on application and a moisturising feel. This variant is suited for people who want sun protection with added skin conditioning, particularly those with drier skin or those using sunscreen in air-conditioned environments where skin loses moisture.

Why East24 works as everyday sun hygiene

Both variants are designed for daily use, not just beach days or outdoor activities. Because UVA is present year-round and passes through windows and clouds, the most protective habit is applying sunscreen every morning as part of a routine, the way you wash your face or brush your teeth.

East24 is positioned as a family sunscreen, meaning it is designed for all members of a household: adults, older children, and seniors. Each person has different skin and different UV exposure patterns through the day, and both formulations are suitable for regular, repeated use.

How much UV exposure does India get?

India's location between 8 and 37 degrees north latitude means most of the country receives high UV radiation for a large portion of the year. Cities closer to the equator, like Chennai, Kochi, and Bengaluru, experience high UV index values for almost the entire year.

UV index explained

The UV index (UVI) is a scale developed by the World Health Organization to indicate the intensity of UV radiation at a given location and time. It runs from 0 (no risk) to 11+ (extreme risk).

According to data from the WHO and national UV monitoring, several Indian cities regularly record UV index values of 8 to 11+ during summer months. Even in winter, the UV index in southern India rarely drops below 5, which is still in the moderate-to-high range requiring active protection.

Sources and references

The following sources were used in the research and writing of this article:

1. World Health Organization. Ultraviolet radiation and health. who.int/news-room/fact-sheets/detail/ultraviolet-radiation

2. Skin Cancer Foundation. UVA and UVB. skincancer.org/risk-factors/uv-radiation

3. American Academy of Dermatology Association. Sunscreen FAQs. aad.org/public/everyday-care/sun-protection/sunscreen-patients/sunscreen-faqs

4. Bureau of Indian Standards. IS 16798: Cosmetics — Sunscreen products — Methods of test. Bureau of Indian Standards, New Delhi.

5. Diffey, B. L. (2001). When should sunscreen be reapplied? Journal of the American Academy of Dermatology, 45(6), 882 to 885.

6. Pinnell, S. R. et al. (2000). Cutaneous photodamage, oxidative stress, and topical antioxidant protection. Journal of the American Academy of Dermatology, 43(1 Pt 1), 1 to 4.

7. World Health Organization. The known health effects of UV. who.int/uv/health/en

8. Matsumura, Y. and Ananthaswamy, H. N. (2004). Toxic effects of ultraviolet radiation on the skin. Toxicology and Applied Pharmacology, 195(3), 298 to 308.

9. Open-Meteo UV index data. open-meteo.com

Common questions about UVA and UVB

Can I get sun damage indoors? Yes. UVA rays pass through standard glass windows. If you sit near a window for extended periods during the day, your skin is receiving UVA exposure. Applying sunscreen before sitting near a window, including in offices and cars, provides meaningful protection.

Do dark-skinned people need sunscreen? Yes. Darker skin has more melanin, which provides some natural protection against UVB, but it does not block UVA. DNA damage from UV radiation occurs in all skin tones. The risks of cumulative UV damage, including long-term skin changes and increased skin cancer risk, apply across all skin types.

Is SPF 50 enough, or should I use SPF 100? SPF 50 blocks 98% of UVB rays. SPF 100 blocks approximately 99%. The difference is marginal in practice, especially if you apply sunscreen correctly and reapply it. SPF 50 PA++++ with correct application and reapplication is a reliable and practical choice for everyday use in India.

How much sunscreen should I use? Dermatologists recommend approximately 2 mg per square centimetre of skin for the face alone. In practical terms, this is about half a teaspoon for the face and neck. Most people use significantly less than this, which reduces the effective SPF they receive.

Does sunscreen expire? Yes. Sunscreen has a shelf life, typically printed on the packaging. After this date, the UV filter molecules may degrade and the product will not provide the rated protection. Using expired sunscreen is not recommended.

Should I apply sunscreen even on cloudy days? Yes. Clouds reduce UVB by some amount, but UVA passes through clouds with very little reduction. On a fully overcast day, up to 80% of UV radiation still reaches the skin's surface.

Does sunscreen prevent Vitamin D production? This is a common concern. Research shows that in real-world conditions, most people do not apply sunscreen with full coverage or do not reapply it consistently, so some UVB reaches the skin and Vitamin D synthesis occurs. In countries with high UV like India, adequate Vitamin D can generally be maintained even with daily sunscreen use. If you have specific concerns about Vitamin D levels, speak with a doctor.

What does "broad spectrum" mean on a label? Broad spectrum means the sunscreen has been tested and confirmed to provide meaningful protection against both UVA and UVB rays. In India, this is represented by the SPF (for UVB) and PA++++ (for UVA) combination on the label.

Is PA++++ better than PA+++? Yes. Each additional plus sign represents a significantly higher level of UVA protection. PA++++ offers the highest commercially available UVA protection grade, with a protection factor of 16 and above. For year-round use in India, PA++++ is the recommended standard.

Closing

The sun does not change what it sends toward Earth each day. UVA rays arrive in abundance, all year, through clouds and windows, going deep into the skin. UVB rays arrive in smaller quantities but with enough energy to cause sunburn and direct DNA damage. Both are present in India throughout the year, and both are worth protecting against.

Understanding the difference between UVA and UVB is not about fear. It is about clarity. When you understand what these rays do and when they are present, applying sunscreen in the morning becomes as automatic as any other basic hygiene habit. It is a small action with a long-term effect that compounds over years.

The label on a sunscreen bottle, once you know how to read it, tells you exactly what you are getting. SPF 50 for UVB. PA++++ for UVA. Broad spectrum for both. These three markers together tell you that the product is doing the full job.

Sun hygiene is not seasonal. It is not situational. It is a daily basic, the way brushing teeth is a daily basic. The skin you have at 50 is being shaped by the choices you make today. Daily broad spectrum sunscreen is one of the simplest and most evidence-backed things you can do to protect it.