Costa Rica Study: Sunscreen Still Safe Despite Tiny Heat Effect

Scientists in Costa Rica just made it easier for people working in the heat to stay safe from both the sun and rising temperatures.

University of Costa Rica researchers discovered that some water-resistant sunscreens may slightly reduce the body's cooling ability during exercise in hot weather. The effect is tiny: internal body temperature rose by just 0.2 degrees Celsius after one hour of cycling in laboratory conditions mimicking Costa Rica's tropical climate.

The research team stressed this small difference should never stop anyone from using sunscreen. Sun protection remains critical for preventing sunburn and blocking harmful ultraviolet radiation.

Fifteen physically active university students completed the study by cycling for one hour in a climate-controlled chamber set to 35°C (95°F) with 55% humidity. Half the time they wore water-resistant sunscreen covering 85% of their bodies, and half the time they exercised without it.

When wearing sunscreen, participants felt slightly thirstier and showed the modest temperature increase. Everything else stayed the same: skin temperature, sweat production, heart rate, and body mass showed no meaningful differences.

The researchers believe certain sunscreen ingredients create a film that may interfere slightly with sweat evaporation. Since evaporating sweat cools our bodies, even a small reduction allows heat to build up gradually over time.

An earlier study found that sunscreens containing dimethicone, a silicone that creates water-resistant protection, reduced local sweating more than other formulas. This discovery led the team to investigate whether protective films might affect heat release.

The Bright Side

This research gives outdoor workers, athletes, and anyone spending time in hot climates better tools to stay safe. The findings are especially valuable in Costa Rica, where agricultural workers, construction crews, and hikers regularly face intense heat and humidity for hours at a time.

The solution is straightforward: treat sun protection and heat safety as partners, not competitors. People can keep wearing sunscreen while also drinking plenty of water, taking regular breaks, finding shade, and choosing lightweight, breathable clothing.

These simple precautions matter far more than the tiny temperature difference measured in the lab. The study doesn't suggest changing sunscreen habits but rather adding smart heat management strategies alongside existing sun protection.

The research team published their findings in the Journal of Science and Medicine in Sport, giving outdoor workers and health officials evidence-based guidance for staying safe in tropical conditions.

Costa Rican scientists just proved you can protect your skin and manage heat at the same time.