A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave.
Some causes of cold intolerance are: 1  Anemia. 2  Anorexia nervosa. 3  Blood vessel problems, such as Raynaud phenomenon.  Chronic severe 1  illness. General poor health.  Underactive thyroid 1  (hypothyroidism) Problem with the hypothalamus (a part of the brain that controls many body functions, including body temperature)
The common cold or seasonal flu is most often caused by a viral infection of the nasal passages, which causes the mucus build up in the nose, throat, and sometimes the chest, which again, drains down the back of the throat, similar to post-nasal drip, but is caused by the infection of the sinuses, lungs, or upper airways, and not simply allergies.