Dr Joshua Adebayo
White blood cells are like the security agents (such as police) of the body. They are there to ensure that no intruder enters the body to cause problem for the body. They move around to ensure this, just as police patrol to be sure no criminal is hiding somewhere.

When there is an intruder in form of infection such as bacteria or viruses, sometimes, parasites, they request for reinforcement to be able to round up and kill the intruder. This is the most common reason why white blood cell number increases in the body.

Other causes not related to these are pregnancy and leukaemia / lymphoma (cancer of the white blood cells). In pregnancy, there is increase in production of white blood cells to protect the mother against infections in pregnancy. However, in leukaemia or lymphoma, there is abnormal proliferation of white blood cells due to loss of control on the rate of division of white blood cells. So, they continue to divide without regulation.

These are some of the reasons there may be increment in the number of white blood cells