Baldness involves the state of lacking hair, most often on the head. The most common kind of baldness is what is called "male pattern baldness" in which the crown of the head and top lose hair. This is medically known as androgenic alopecia. This type of alopecia can also occur in women, but they seldom lose all their hair; it just gets thinner all over and the hairline does not recede. This type of alopecia is hereditary and accounts for 99% of hair loss.
There are also other types of alopecia. For instance, alopecia areata is manifested sometimes in patches on the head, often with one side more affected than the other. Hair loss tends to be rather rapid. Other alopecias occur after very high fevers or severe illness. high doses of Vitamin A, or retinols. This hair loss is often temporary, however.
So, baldness is the state of lacking hair, while alopecia is a medical condition which causes various types of baldness.
Baldness is simply not having hair on your head. Baldness can be caused by a number of things. Perhaps the most common cause of baldness is being male. Many men have what is called male pattern baldness.
By contrast, Alopecia is a particular condition that can cause partial or even complete baldness. So some people who are bald are bald because of Alopecia -- Alopecia is one cause of baldness.
The cause of Alopecia is not completely understood. It appears to be genetic and seems to be caused by a problem with the autoimmune system.
There is no difference between the terms 'baldness' and 'alopecia.' Both mean the same - partial or complete absence of hair on the scalp.
'Alopecia' is the medical term for the common word 'baldness.'
MedicineNet.com defines 'alopecia' as ,
The word "alopecia" comes from the Greek "alopex" for "fox." Foxes are less furry when afflicted with a skin disease (the "mange") which causes them to lose their hair. When a fancier word for "baldness" was sought, the mangy fox supplied it -- "alopecia" or, if you wish, "fox-mange" -- not a very positive image to associate with baldness!
There are various types of alopecia based on the amount of hair loss and the pattern of hair loss. Causes and treatment for the various types of alopecia vary accordingly.