If you are suddenly beginning to lose hair for what seems to be no good reason, you will want to see a dermatologist. It may seem like a strange place to go since they usually deal with the skin. They can help you with hair loss as well. If you are having other symptoms that lead them to believe you may have another more serious issue then they will refer you.
There are health problems such as those with the thyroid that can cause hair loss. Deficiencies in your diet might also be a cause. Pregnancy is also a cause of hair loss. It is usually after having a baby that you might notice hair loss in large quantities. This is fairly normal, but the first two should definitely be looked into. If you feel you are even losing too much after pregnancy, contact your doctor for a referral to a local dermatologist.
Do not be afraid to go to a dermatologist for fear you have something serious. Most likely it will be something simple that can be corrected, but it is best to get a professional opinion. There are over-the-counter supplements that might help those who have just had a baby, but you should discuss specifics with your doctor especially if you are still breastfeeding.
As a man, you might not worry about losing your hair. If you notice though that it does not seem to run in your family then you may have a good reason to check with a dermatologist. This is especially the case if your eyelashes and eyebrows start to go away as well as the hair on your head. This could be a sign of a thyroid condition other than normal hair loss.
As a woman, your situation is totally different. Usually you do not see women balding as often as you see men. It can happen though, and when it does, it most likely is very disconcerting. You may be embarrassed to talk to anyone about it. If it is noticeable though, one of your friends might ask about your health. You should ask yourself about it as well. It will not hurt you to go to a dermatologist just to get things checked out. If you would rather not go to them, start with your primary care provider to see if they can do blood work on you.
Never put off embarrassing issues. Sometimes your life can depend on making the right choice in matters like this, but most times, it will probably be a quick fix.