A cyst is an abnormal closed, hollow, and membranous sac filled with air, bodily fluids, keratin, and/or pus if the cyst has ever been infected. Follow Us: Instagram - https://www.instagram.com/contourderm/ Twitter - https://twitter.com/contourderm/ LinkedIn - https://www.linkedin.com/company/contour-dermatology-&-cosmetic-surgery-center Snapchat - @contourderm Pinterest - https://www.pinterest.com/contourderm760/