This is just a skin infection and is called as Dermoid Sinus that is common in pets due to infection of skin so you must give him some anti-biotic so that he can be cured from this disease.

 Get him to the vet, this could end up being very serious, and might put his health at risk. Hope this helps.

 Take it to the vet immediately my hamster had dermatitis and I didn't catch it in time and he died.