Sun and heat safety on Koh Samui

The tropical sun on Koh Samui is stronger than most visitors expect, and UV levels are high year-round, including on overcast days. Daytime temperatures commonly exceed 32-34°C with high humidity, and the hottest stretch is roughly March to May. The common consequences are mundane but trip-ruining: bad sunburn on day one, dehydration, heat exhaustion with headache, dizziness and nausea, and in severe untreated cases heatstroke, which is a medical emergency. Prevention is straightforward. Drink water regularly beyond thirst, carry a bottle, and use oral rehydration salts (a few baht at any pharmacy) if you have been sweating heavily or have an upset stomach. Apply broad-spectrum SPF 50+ sunscreen every morning and reapply after swimming; wear a hat, sunglasses and light long sleeves for midday exposure. Plan physical activities, temple visits, hikes to waterfalls or viewpoints, for early morning or late afternoon, and treat 11:00-15:00 as shade or pool time. Be extra careful with children and older travellers, who dehydrate faster. Alcohol and caffeine increase fluid loss, so balance beach-bar days with water. If someone shows confusion, stops sweating, or collapses in the heat, move them to shade or air-conditioning, cool them with water and fanning, give fluids only if fully conscious, and call 1669 if they do not improve quickly or lose consciousness. See the health category for more on recognising heat illness.

Summary

Koh Samui is hot and humid all year, with daytime temperatures regularly above 32-34°C and strong tropical sun even when cloudy. Sunburn, dehydration and heat exhaustion are among the most common tourist health problems, and all are easily prevented with water, shade timing and SPF 50+ sunscreen.

Key facts

• UV is strong year-round, including on cloudy days; SPF 50+ is advised
• Daytime temperatures regularly exceed 32-34°C with high humidity
• Hottest period is roughly March to May
• Dehydration and heat exhaustion are among the most common tourist health issues
• Heatstroke (confusion, collapse, hot dry skin) is a medical emergency: call 1669

Local tips

• Do hikes and temple visits before 10:00 or after 16:00
• Carry water on every outing; pharmacies sell cheap oral rehydration salts
• Reapply sunscreen after every swim; Thai sun burns through one morning application
• Alternate alcoholic drinks with water at the beach