What you may have heard
Standing too close to the microwave can increase your risk of developing cancer.
What science tells us
Microwaves do not emit enough radiofrequency radiation to be harmful to humans (ACS). Microwave ovens are designed so that the microwave radiation is contained within the oven itself. The oven only creates microwaves when the door is shut, and the oven is turned on.
Epidemiological Evidence
When microwave ovens are in good condition and are used according to instructions, there is no evidence that they pose a health risk to people.
Laboratory Evidence/Supporting Evidence
There are very limited animal or laboratory studies that look into the relationship between microwaves and cancer.
IARC Carcinogen Classification:
Group 2B (possibly carcinogenic: if microwave is broken/open)
How to reduce your risk
The best way to reduce your risk is to ensure that your microwave is in good working condition. Replace your microwave whenever it is damaged, as this might allow radiation leakage that could be harmful to humans, if not addressed.
Bottom line
Using a microwave is not risky, as long as the microwave is in good condition.