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: A synthetic form of progesterone that is similar to the hormone produced naturally by the body. Sperm: A cell produced in the male testes that can fertilize a female egg. Uterus: A muscular organ located in the female pelvis that contains and nourishes the developing fetus during pregnancy.t also can be used by itself in progestin-only pills and the birth control injection. The birth control implant and the hormonal intrauterine device also are progestin-only forms of birth control and are discussed in FAQ184 Long-Acting Reversible Contraception (LARC): IUD and Implant.