Dear Lena,

Normally, you shiver when you feel cold, but fever, illness, or other harsh conditions can also set off the shivers. When you shiver, your muscles contract and relax quickly, causing uncontrollable quivering all over your body. In the case of a reaction to the cold, a drop in skin and body temperature will signal the hypothalamus. Once activated, this part of the brain will stimulate muscle contractions (the shivering reflex) in order to warm up your body. After enough heat has been produced, the shivering stops.

Goosebumps are caused by the pilomotor reflex. When you're exposed to cold temperatures or emotional stimuli, or if your skin's irritated, this reflex triggers an involuntary muscle contraction that raises the hairs of your skin, producing goosebumps. The response to cold, known as piloerection, helps keep air near the skin, thereby retaining heat for the body.

Alice

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