What is the UV Index? The overlooked number behind sun damage risks

Even on cooler or cloudy days, harmful UV radiation can remain high, making the UV Index a critical tool for daily protection and long-term skin health

As India experiences longer summers and more frequent heatwaves, another invisible threat is intensifying alongside the heat — ultraviolet radiation. And unlike rising temperatures, it often goes unnoticed. 

While people track temperature and air quality, very few pay attention to the UV Index, which directly reflects the risk of skin damage. Experts say this gap in awareness could have long-term consequences, making it essential to understand what the UV Index really means and how it is measured.

What is the UV Index and how is it measured scientifically?

“The UV Index (UVI) is a standardised measure of erythemally effective ultraviolet radiation reaching the Earth’s surface, indicating the potential for biological skin damage, primarily from UVB and UVA wavelengths,” says Dr Sonia Tekchandani, dermatologist, founder & medical director of TenderSkin International. In simple terms, “erythemally effective ultraviolet” refers to the portion of UV radiation that is most capable of causing sunburn and skin damage. 

 

She explains that scientists measure UV radiation in two key ways.

• On the ground, specialised instruments such as spectroradiometers capture real-time UV intensity at specific locations
• For broader forecasts, satellite data and atmospheric models are used

“These models incorporate variables such as solar zenith angle, ozone concentration, cloud cover, altitude, aerosols, and surface reflectivity,” she adds. 

While ground devices tell you what is happening right now, forecast models help predict what is coming.

Who measures the UV Index in India and what does the scale mean?

In India, the India Meteorological Department (IMD) monitors UV radiation, aligning its reporting with global standards set by the World Health Organization and the World Meteorological Organization. 

The UV Index follows a universal scale from 0 to 11+, which indicates risk:

• 0–2: Low
• 3–5: Moderate
• 6–7: High
• 8–10: Very high
• 11+: Extreme

“Importantly, the UV Index reflects the risk of sunburn and cumulative skin damage, not ambient temperature,” Dr Tekchandani notes. 

This means you can still experience high UV exposure on a cool or cloudy day.

What factors determine daily UV Index levels?

Several environmental factors influence how much UV radiation reaches you. These include:

• Latitude: Regions closer to the equator receive stronger UV
• Time of day: Peak exposure occurs when the sun is overhead
• Altitude: Higher elevations mean thinner atmospheric protection
• Ozone levels: Less ozone allows more UVB to pass through
• Cloud cover: Can reduce, but not eliminate, UV exposure
• Pollution: Alters how UV is absorbed or scattered
• Surface reflection: Sand, water and concrete can intensify exposure

“From a dermatological standpoint, these variables explain why UV exposure can remain high even in non-obvious conditions,” she says.

When is UV radiation highest and how can you track it?

In India, UV radiation typically peaks between 10 am and 4 pm, especially during the summer months from March to June. 

However, exposure remains moderate to high throughout the year due to the country’s geographic location. 

Dr Tekchandani points out that UVA radiation is constant and can penetrate clouds and glass, contributing to damage even indoors  .

“UVA rays do pass through glass and contribute to gradual skin ageing and pigmentation. However, the intensity indoors is diluted compared to direct sun exposure outdoors,” adds Dr Akanksha Agarwal, founder-director and head of aesthetic services, Centre for Aesthetics (CFA), Gurgaon. 

To stay informed, you can check UV levels through:

• IMD updates
• Weather apps with UV forecasts
• Global UV monitoring platforms

How high are UV levels across Indian cities today?

Recent observations suggest that UV exposure across Indian cities is already in the high to extreme range in March, even before peak summer.

• Bengaluru: Around 13 (extreme)
• Chennai: 9–10 (very high)
• Mumbai: Around 8–9 (high)
• Delhi: Around 8 (high)
• Hyderabad: 9–10 (high)
• Multiple cities in Kerala: 8–10 (very high to extreme)

Seasonally, India remains a high UV zone:

• Winter: Moderate to high
• Pre-summer: High to very high
• Peak summer: Very high to extreme
• Monsoon: Variable but still relevant

This highlights that UV exposure is not just a summer concern but a year-round reality.

How is climate change increasing UV exposure risks?

Climate change is not necessarily increasing UV radiation uniformly, but it is intensifying how much exposure people actually get. 

“Rising temperatures increase time spent in lighter clothing and outdoor environments, leading to greater cumulative UV exposure,” Dr Tekchandani explains. 

Changing cloud patterns, fluctuating pollution levels and ozone variations also play a role. 

From a medical perspective, the concern is cumulative exposure, which increases risks of photoaging, pigmentation and even skin cancer over time.

What are the hidden health risks beyond sunburn?

Sunburn is only the most visible effect of UV exposure. The deeper damage is often silent and long-term. 

“UV exposure leads to cumulative molecular and structural skin damage, often clinically silent initially,” she says. Key health impacts include:

• DNA damage and increased cancer risk
• Premature ageing and collagen breakdown
• Pigmentation disorders such as melasma
• Immune suppression
• Eye damage, including cataracts and retinal injury

These effects build over time, making prevention critical.

Why is awareness of UV Index still low in India?

Despite high exposure levels, UV awareness remains limited. 

Experts attribute this to a common misconception where people associate sun damage with heat. However, UV radiation operates independently of temperature. 

Other factors include limited UV reporting in daily forecasts, delayed visible effects, and low adoption of routine sun protection practices.

How can you protect yourself from daily UV exposure?

Experts recommend a combination of daily habits rather than occasional precautions:

• Use broad-spectrum sunscreen (SPF 30 or higher)
• Apply adequately and reapply every 2–3 hours if outdoors
• Wear protective clothing, hats and UV-blocking sunglasses
• Avoid peak sun hours when possible
• Seek shade during midday
• Use antioxidants like vitamin C to combat oxidative stress
• Follow protection routines year-round

“Regular and correct photoprotection is the most effective strategy to prevent photoaging, pigmentary disorders, and UV-induced skin damage,” Dr Tekchandani emphasises. 

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This report is for informational purposes only and is not a substitute for professional medical advice.