Do guinea pigs struggle in summer heat? What temperature is dangerous?

Short answer: very much so. The ideal range is 18–26°C (64–79°F); above 28°C (82°F) cool them actively, and above 30°C (86°F) heatstroke becomes a real risk.

1. Placement — away from direct sun through windows and stuffy corners, with good airflow.

2. Cooling — air conditioning or a dehumidifier; marble or ceramic tiles; a frozen bottle wrapped in a towel beside the cage.

3. Hydration — add an extra water source and water-rich vegetables like cucumber.

4. Avoid — spraying or bathing them, or a fan blowing directly for long periods.

5. Emergency signs — open-mouth breathing, lying flat, drooling or hot limbs: move to shade and see an exotic-pet vet immediately.