Re: When the weather is cold,our nose turns red, why?

Lim, sorry about the delay.

When your skin temperature falls below about 10C, the surface blood vessels dilate (get wider) rather than constrict (get narrower), this is to increase bloodflow and the unloading of oxygen. If the temperature falls further, periods of blood vessel dilation alternate with periods of constriction. This is because your body is trying not to lose heat from the extremities (i.e. your nose), but at the same time wants to supply the skin with blood for oxygen and nutrients. This phenomenon explains the red cheeks and nose characteristic of frosty weather. Eventually, however, the body is unable to keep the core temperature at 37C and so must 'sacrifice' some of the less important parts which include your fingers, toes and ears and stops the dilation of the blood vessels to these parts, and the skin falls to the surrounding temperatures when frost nip or frost bite may occur. If the core temperature continues to drop to below 25C hypothermia or even death can result.

Try the following link for more information:
www.coolantarctica.com/Antarctica%20fact%20file/science/cold_humans.htm

Hope this helps,

Sean