Cold air weakens winter natural defenses, increasing infection risk. Modern research shows low temperatures do not directly cause illness; instead, they help viruses survive longer in the air and reduce the body's natural barrier in the nose. Cold, dry air narrows blood vessels, slowing local immune response, while indoor crowding and poor ventilation allow viral particles to linger. Reduced sunlight exposure during winter also lowers vitamin D levels, further weakening immunity. Health experts recommend regular ventilation, humidifiers, and adequate vitamin D to protect against seasonal infections.
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