Anal fistulas are caused due to an infection that starts in an anal gland. The reasons for the infection can be many, right from anal sex to some surgery. If this infection results in pus then an abscess is formed that drains spontaneously. This ultimately results in a fistula that forms a tunnel under the skin. This fistula is connected with the infected gland hance it secretes bad-smelling pus. At Vithai Piles Treatment Centre we offer laser treatment of fistulas. For appointments, do visit our website http://www.ladypilesdoctorpune.com/.