If you see that cats lose their hair, do not leave it unattended. After all, the reason of hair loss is not always a seasonal molt.
Cats shed twice a year: fall and spring. You need to follow the diet of its power during this period, so the cat had all the necessary minerals and vitamins. Moreover, living conditions for the cats to be good, there should be no dampness and drafts, so as not to have worse hair loss.
If hair falls out in any specific areas, then it is probably a fungal disease.
Another reason might be the hormonal background of the animal because of the medication that you she could give him, to reduce sexual desire in the spring. These drugs are quite harmful for cats: it becomes sluggish, apathetic, lethargic, she has impaired vision and skin condition.
You need to check for the presence of animal parasites such as lice or voloskami. Allergy in cats can also cause loss of hair.
If hair falls out is not during the shedding season, you need to contact your veterinarian to determine a diagnosis and prescribe treatment that should be followed.