The sensation of hair standing on end is often associated with a buildup of electrical charge in the air, which can occur before a lightning strike. When there is a significant electrical field present, such as during a thunderstorm, the charge can affect objects and even the human body.
When the electric field in the atmosphere becomes strong, it can induce an opposite charge on objects, including the hair on your body. As a result, individual hairs may repel each other, causing them to stand up or appear to "stand on end." This phenomenon is known as piloerection or pilomotor reflex.
While hair standing on end can be an indication of an impending lightning strike, it is not a foolproof method of predicting lightning. Other warning signs, such as darkening skies, rumbling thunder, and the smell of ozone, are more reliable indicators of an approaching lightning storm.
It's crucial to remember that if you find yourself in a thunderstorm, you should seek shelter indoors or in a substantial, enclosed structure to reduce the risk of being struck by lightning.