Cold

Cold refers to low temperature in the environment or a perceived lack of warmth. In physics, temperature measures the average kinetic energy of particles; cold is the state of having relatively low thermal energy compared with a reference temperature. Because temperature is relative, what is considered cold depends on context, season, and the observer’s physiology.

Humans perceive cold when skin receptors detect low ambient temperatures. The body responds with vasoconstriction to conserve heat and shivering to generate heat. Prolonged cold exposure can impair judgment and coordination and may lead to hypothermia or frostbite, especially in wet or windy conditions or at very low temperatures.

The common cold is a viral infection of the upper respiratory tract. It is not caused by cold weather itself, but transmission is facilitated in crowded and dry environments. Rhinoviruses are the most frequent cause; other viruses include coronaviruses and adenoviruses. Symptoms typically include nasal congestion, sore throat, cough, and sometimes fever. Illness usually lasts seven to ten days. There is no cure; treatment is supportive, and antibiotics are not effective against viruses. Prevention centers on hand hygiene, respiratory etiquette, and avoiding close contact with infected individuals.

In addition to weather, cold is used in various contexts. A cold chain describes the maintenance of low temperatures for perishable goods during storage and transport. Cryogenics studies materials at ultralow temperatures. More generally, cold is a common seasonal descriptor for winter in temperate regions.