Many people believe going outside with wet hair will cause them to become ill with the cold or the flu. The truth is this is a myth. You can safely go outside in cold and warm weather safely without becoming sick.
The reason why it is safe to go outside with wet hair is because the only way an illness is caught such as the cold or flu is by coming into contact with airborne viruses and bacteria. You simply can not get sick from not drying your hair before you go outside.
People believe this myth because heat is where we tend to lose the most body heat. People figure if our head is full of wet hair and we go outside into the cold we will lose even more body heat which weakens our immune systems and makes us more vulnerable to catching the bug. This is simply not true either. So, for those of you who have been outside with wet hair and end up getting sick that night or the day after is because you came in contact with an airborne bacteria or a virus and not because your hair was wet.
One of the things that will happen and could happen is your hair could freeze if you go out with wet hair on days when it is below freezing outside. On cool days if you go outside with your hair wet you will simply have a cold head and you will feel colder. The other thing that could happen when you go outside with your hair wet on warm days is your hair will become very frizzy. On a dry windy sunny day your wet hair will actually dry nicely and naturally and it is better for your hair than using a hair drier. It is simply impossible for you to get sick if you do decide to go outside with wet hair in any type of weather.
So, yes you can safely go outside with wet hair on any type of day and not get sick. Airborne germs are what make us sick and not our wet hair. However, I still believe it is best to blow dry wet hair before heading outside in colder weather, but if it is warm and sunny why not. Your hair will just be dried naturally by the warmth of the sun and airy breeze.