Looking at Propecia and alopecia areata
In theory, this is relatively easy to identify because, as its popular name "spot baldness" suggests, the first stages of the conditions are usually the emergence of distinct bald areas. Since male pattern baldness begins to show a distinctive area of loss, the two conditions should be easy to distinguish. However, since both may be "symptomless", i.e. there are no accompanying indications of cause, men in the right age bracket should pause for a short period to ensure the spots do not grow into the characteristic M shape of the male pattern. So what exactly is alopecia areata?
You are likely to find hair falling out and forming distinct bald patches. The scalp will look and feel quite normal (although a very small number do report occasionally feeling a slight itchiness) and there are no obvious scars or other marks. Over time, the patches can expand and result in a completely bald head. In about 2% of all cases, hair is lost from the entire body. In the early or middle stages of the disorder, this can make the face look odd because, for example, the hairline forming the eyebrows may be broken and bald patches can appear in a beard or mustache.
Difficult choices to preserve your appearance can be produced when your hair is being lost on visible parts of the body in unpredictable areas. In the early stages, there are periods of loss followed by quite intense periods of regrowth. The timing of each period may vary between a few weeks and several months. It's therefore essential not to panic and rush to have some of the treatments on offer. For example, all suggestions of hair transplants should be resisted at the first signs of loss. If you are going to experience periods of loss and regrowth, paying for transplants could be a complete waste of money as different parts of the head might be affected sequentially. However, you should be warned that the regrown hair can be white and only later recover its color.
Although it can make your life a miserable one it does mean that alopecia areata is not in any way life threatening. The lack of any consistently effective treatment can also make this worse. For the record, there are no scientifically reliable trials for any treatment and no evidence of success although there's some anecdotal evidence on the successful use of a 308-nm Excimer laser. It will be interesting to see whether these claims are taken as justifying a full clinical trial.
Putting this together, the word to the wise is to wait a short period if hair begins to fall at the front of the scalp. This could be the first signs of the characteristic shape forming or it could be one or more bare patches emerging. Obviously hair loss on areas of the scalp not usually part of the pattern should be ignored. Using Propecia is not going to help. It's not going to cause you any loss of effectiveness to wait a few weeks before beginning Propecia to confirm which variety of loss you have.