Peritonsillar Abscess Overview. A peritonsillar abscess forms in the tissues of the throat next to one of the tonsils. An abscess is a collection of pus that forms near an area of infected skin or other soft tissue. The abscess can cause pain, swelling, and, if severe, blockage of the throat. If the throat is blocked, swallowing, speaking, and even breathing become difficult. 1  When an infection of the tonsils (known as tonsillitis) spreads and causes infection in the soft tissues, a peritonsillar abscess may result.