Warts are caused by a viral infection known as human papillomavirus, or HPV for short.  As it stands now, there are over 120 types of HPV circulating in the human population today. 

Different types of warts are caused by various types of the HPV virus.  For example, the 1 and 3 strains of human papillomavirus are the most common and they are usually the culprits when someone develops a common wart.
 

Developing specific types of warts depends not only on the type of HPV but also on your immune system.  Every person's immune system reacts differently to HPV so there are some people that may not develop warts even if they have come in direct contact with the virus.

 

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