Pigs are particularly vulnerable to heat stress as they lack functional sweat glands and rely on respiratory panting, conduction, and wallowing for thermoregulation. Upper critical temperature thresholds are 25C for sows and 28C for finishing pigs. Heat stress reduces feed intake, growth rate, and reproductive performance while increasing mortality risk in extreme conditions. Wallowing in mud is a highly motivated natural thermoregulatory behaviour; provision of wallows in outdoor systems significantly improves welfare in hot conditions. Indoor cooling systems include sprinklers (wetting skin for evaporative cooling), nose coolers (chilled air delivered to snout level), and shading. Research demonstrates sprinkler cooling reduces respiration rate and rectal temperature within 30 minutes. Climate change is extending heat stress periods in temperate regions, making cooling infrastructure investment increasingly necessary. Welfare certification schemes now require cooling provision above defined temperature thresholds.