Egg Activation

Reviewed by Ashley Wong, MS, Clinical EmbryologistCheckmark
Published: November 15, 2017

What Does Egg Activation Mean?

Egg activation is a series of biological and chemical processes that occur in an egg once a sperm has entered the egg and prior to fertilization. These processes allow for the DNA from an egg to mix with the DNA from a single sperm.

Once the egg and sperm combine their DNA, fertilization has taken place and an embryo starts to form. Egg activation must occur in order for the egg to be successfully fertilized.

FertilitySmarts Explains Egg Activation

Female bodies have all of the eggs they will ever have at birth. These eggs go through a certain phase of development before birth, at puberty, and at the time of ovulation. This process is called oogenesis and these phases prepare an egg for fertilization by sperm.

Polyspermy Block

There are multiple complex processes that happen when an egg is activated. First, the outer layer of the egg hardens, after a sperm has entered, to prevent additional sperm from entering the egg, creating a process called polyspermy block.


The egg must also continue through a process called meiosis. This is a multi-step process by which the standard 46 chromosomes are shuffled and decreased to half the number, at 23 chromosomes. These 23 chromosomes will combine with the 23 chromosomes of the sperm during fertilization to make a zygote, a single cell that will divide and transform into an embryo.


Oocyte Activation

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