Why do I get a headache as soon as I turn on the air conditioning?

Headaches triggered immediately upon turning on the air conditioner may be caused by cervical spondylosis, vasoconstriction, or a common cold.

1. Cervical Spondylosis

Long-term heavy physical labor may cause persistent fatigue and injury to the neck muscles. When exposed to cold air from the air conditioner, the occipital and cervical muscles may go into spasm; in severe cases, even the superficial soft tissues of the head may spasm. This can lead to insufficient blood supply via the vertebral arteries, resulting in cerebral hypoperfusion. Cerebral hypoperfusion, in turn, may manifest as headache.

2. Vasoconstriction

Headaches occurring immediately after turning on the air conditioner may result from the low ambient temperature causing systemic vasoconstriction. Constriction of small cerebral vessels may impair cerebral blood flow, thereby triggering headache.

3. Common Cold

Excessive temperature differences—such as extremely low outdoor temperatures in winter coupled with excessively high indoor temperatures—may predispose individuals to the common cold. During a cold, patients often experience sleep deprivation and systemic fever. Fever can induce dilation of intracranial arteries and trigger localized vascular spasm, potentially leading to headaches upon exposure to cool air from the air conditioner.