The risk of ill-health, including loss of life. Health risk is a very general term which includes the potential for both physical and emotional damage. There are a myriad of health risks as there are many ways one can suffer physical or emotional damage.
Stepping out of the house in the morning.
You are struck down by a car (or become exposed to pollution, or come in contact with nasty germs). This leads to ill-health requiring medical attention for three months. During this time you are in a lot of physical pain and feel emotionally depressed.
You run into a stranger on the subway, engage in small talk, and hit it off. You continue to communicate for a few weeks, and then he offers you your dream job. Later, he introduces you to your future spouse.
Physical risk refers to just those risks that may lead to physical damage, unlike the more general term, health risk, which may include physical and emotional damage.
Public health Risk
Public health risk is the risk to communities. Often, when we use the term health risk we explicitly or implicitly think of risk to ourselves or other individuals. When the risks are to larger groups of people, they are viewed as public health risks. Public health laboratories and government departments of health are concerned with the risk to larger populations. Relevant risks include infectious diseases and bio-terror strikes.