This type of OCD refers to the fear of being dirty or poisoned, touching things with germs or other viruses, becoming morally contaminated, or getting / passing an illness from or to another person. It can even be a combination of any of these, and the reason behind these fears can be varied. There are some that fear the negative social or health impacts of viruses such as AIDS, while others do not fear but rather have feelings of disgust or discomfort from contact with dirt, citing it to be an intensely distracting feeling.

The fear can also be about moral or emotional contamination, where the person obsesses about hearing vulgarities, seeing disturbing images, or being near someone they see as morally ‘dirty’. In all of these cases, the sufferer can display the common behavioural compulsions of washing their hands, showering, cleaning their ears, or avoiding places which feel contaminated to them, all of which are mental rituals they engage in to neutralise this perceived threat of contamination.