An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body.Such reactions are called allergies.hen an allergen enters the body of an individual that is predisposed to allergies, it triggers an immune reaction and the production of antibodies. These allergen antibodies migrate to mast cells lining the nose, eyes and lungs.
Progestins are synthetic progestogens, medications that have effects similar to those of progesterone. The two most common uses of progestins are for hormonal contraception (either alone or with an estrogen), and to prevent endometrial hyperplasia from unopposed estrogen in hormone replacement therapy.
Progestin is a form of progesterone, a hormone that plays a role in the menstrual cycle and pregnancy. Progestin is used in combination with another hormone called estrogen in combined hormonal birth control pills, the vaginal ring, and the skin patch.