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-Only Pills. You may start the progestin-only pill at any time. Use another method of birth control if you have vaginal intercourse during the first 48 hours of progestin-pill use â protection will begin after two days. Taking the progestin-only pill at the same time each day is essential.ome combination pills contain a few monthsâ worth of active pills. They are specially packaged to reduce the number of periods a woman has each year. Women can also take the active pills in 21-day or 28-day packs continuously to reduce how often they have periods. Progestin-only pills come only in 28-day packs.