More often they are caused by viruses. The symptoms are redness of the throat, painful swallowing and sometimes fever. In these cases you need to take some medications that can decrease your symptoms. Although this condition usually not more serious, if not disappeared three days after the beginning, you should consult your doctor.
If there is a history of rheumatic fever if the fever is high, where they appear white patches or skin rash, goes also to the doctor if could be something more serious.

Anyway, here are some tips for protecting your throat:

On cold days you breathe through your nose and cover your mouth with a scarf. Thus, the inhaled air reaches the pharynx hot and not irritated.