In case of what is known as spot baldness (alopecia areata), round bald spots form relatively quickly. This form of hair loss usually affects children and young adults, but can also recur years later. While the causes have not been entirely clarified, medical professionals believe a misdirected defence reaction of the body aimed at its own hair is to blame.
Whether one is actually suffering from hair loss is best clarified by a doctor, taking into account the duration and severity of loss along with other possible symptoms. This is also the way to find the best treatment method.