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)
Cold sores are caused by the herpes simplex virus (HSV). Most cold sores are caused by the type 1 strain (HSV-1). The type 2 HSV strain (HSV-2) usually causes genital herpes but very occasionally can cause cold sores around the mouth. See separate leaflet called Genital Herpes for more details. A first cold sore usually occurs in childhood.