Mast cells. Mast cells and basophils are generally thought to be the major sources of histamine and can themselves be modulated by histamine as they express H 1, H 2 and H 4 receptors, although how this varies between different mast-cell types is not yet clear.
3. The pill is to be taken soon after unprotected sex. It should be taken preferably within 24 hours and before 72 hours or else the pill may turn useless. 4. I-pill checks pregnancy by preventing ovulation or fertilisation or implantation of the fertilised egg. 5. I-pill is 95 per cent effective if taken in time.
That is why you can take the morning after pill up to three days after having sex. Before fertilization can occur, the sperm must reach the egg. Each egg is only viable for 12 to 48 hours and some sperm can survive for as long as 72 hours, but most can only retain their fertilizing power for 12 to 48 hours.