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)
For the book by Linus Pauling, see Vitamin C and the Common Cold (book) . The common cold is caused by several groups of viruses including rhinoviruses, coronaviruses and respiratory syncytial virus.Colds are the leading cause of doctor's visits and the number one reason for absences from work and school. recent literature review concluded that vitamin C consumption may decrease the duration of cold symptoms, but does not prevent a cold or affect symptom severity. Claims of vitamin C's efficacy in treating the common cold have been criticized by many researchers.