Both sex are equally affected

Any age group can develop a parapheryngeal abscess but it is most commonly seen in children and adolescents. Adults who are immunocompromised are also at high risk.

Infection can occur from:

- Pharynx: acute and chronic infection of tonsil and adenoids

- Teeth: dental infection occurs from lower last molar tooth

- Ear: bezold abscess and petrositis

- Other space: infection of parotid retropharyngeal space

- External trauma: penetrating injuries of neck, injection of local anaesthetic

RPA is usually caused by a bacterial infection originating from the nasopharynx, tonsils, sinuses, adenoids or middle ear. Any upper respiratory infection (URI) can be a cause. RPA can also result from a direct infection due to penetrating injury or a foreign body. RPA can also be linked to young children who do not have adequate dental care or brush their teeth properly.

Even without treatment they rarely result in death as they will naturally break through the skin.

Skin abscesses are common and have become more common in recent years. Risk factors include intravenous drug use with rates reported as high as 65% in this population. In 2005 in the United States 3.2 million people went to the emergency department for an abscess. In Australia around 13,000 people were hospitalized in 2008 for the disease.

PTA usually arises as a complication of an untreated or partially treated episode of acute tonsillitis. The infection, in these cases, spreads to the peritonsillar area (peritonsillitis). This region comprises loose connective tissue and is hence susceptible to formation of an abscess. PTA can also occur "". Both aerobic and anaerobic bacteria can be causative. Commonly involved aerobic pathogens include "Streptococcus, Staphylococcus" and "Haemophilus". The most common anaerobic species include "Fusobacterium necrophorum", " Peptostreptococcus", "Prevotella species", and "Bacteroides".

Retropharyngeal abscess (RPA) is an abscess located in the tissues in the back of the throat behind the posterior pharyngeal wall (the retropharyngeal space). Because RPAs typically occur in deep tissue, they are difficult to diagnose by physical examination alone. RPA is a relatively uncommon illness, and therefore may not receive early diagnosis in children presenting with stiff neck, malaise, difficulty swallowing, or other symptoms listed below. Early diagnosis is key, while a delay in diagnosis and treatment may lead to death. Parapharyngeal space communicates with retropharyngeal space and an infection of retropharyngeal space can pass down behind the esophagus into the mediastinum. RPAs can also occur in adults of any age.

RPA can lead to airway obstruction or sepsis – both life-threatening emergencies. Fatalities normally occur from patients not receiving treatment immediately and suffocating prior to knowing that anything serious was wrong.

Treatment for a nasal septal abscess is similar to that of other bacterial infections. Aggressive broad spectrum antibiotics may be used after the infected area has been drained of fluids.

With prompt treatment, it is possible to cure mastoiditis. Seeking medical care early is important. However, it is difficult for antibiotics to penetrate to the interior of the mastoid process and so it may not be easy to cure the infection; it also may recur. Mastoiditis has many possible complications, all connected to the infection spreading to surrounding structures. Hearing loss is likely, or inflammation of the labyrinth of the inner ear (labyrinthitis) may occur, producing vertigo and an ear ringing may develop along with the hearing loss, making it more difficult to communicate. The infection may also spread to the facial nerve (cranial nerve VII), causing facial-nerve palsy, producing weakness or paralysis of some muscles of facial expression, on the same side of the face. Other complications include Bezold's abscess, an abscess (a collection of pus surrounded by inflamed tissue) behind the sternocleidomastoid muscle in the neck, or a subperiosteal abscess, between the periosteum and mastoid bone (resulting in the typical appearance of a protruding ear). Serious complications result if the infection spreads to the brain. These include meningitis (inflammation of the protective membranes surrounding the brain), epidural abscess (abscess between the skull and outer membrane of the brain), dural venous thrombophlebitis (inflammation of the venous structures of the brain), or brain abscess.

In the United States and other developed countries, the incidence of mastoiditis is quite low, around 0.004%, although it is higher in developing countries. The condition most commonly affects children aged from two to thirteen months, when ear infections most commonly occur. Males and females are equally affected.

Fungi and parasites may also cause the disease. Fungi and parasites are especially associated with immunocompromised patients. Other causes include: "Nocardia asteroides", "Mycobacterium", Fungi (e.g. "Aspergillus", "Candida", "Cryptococcus", "Mucorales", "Coccidioides", "Histoplasma capsulatum", "Blastomyces dermatitidis", "Bipolaris", "Exophiala dermatitidis", "Curvularia pallescens", "Ochroconis gallopava", "Ramichloridium mackenziei", "Pseudallescheria boydii"), Protozoa (e.g. "Toxoplasma gondii", "Entamoeba histolytica", "Trypanosoma cruzi", "Schistosoma", "Paragonimus"), and Helminths (e.g. "Taenia solium"). Organisms that are most frequently associated with brain abscess in patients with AIDS are poliovirus, "Toxoplasma gondii", and "Cryptococcus neoformans", though in infection with the latter organism, symptoms of meningitis generally predominate.

These organisms are associated with certain predisposing conditions:

- Sinus and dental infections—Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (e.g. "Prevotella", "Porphyromonas", "Bacteroides"), "Fusobacterium", "S. aureus", and Enterobacteriaceae

- Penetrating trauma—"S. aureus", aerobic streptococci, Enterobacteriaceae, and "Clostridium" spp.

- Pulmonary infections—Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (e.g. "Prevotella", "Porphyromonas", "Bacteroides"), "Fusobacterium", "Actinomyces", and "Nocardia"

- Congenital heart disease—Aerobic and microaerophilic streptococci, and "S. aureus"

- HIV infection—"T. gondii", "Mycobacterium", "Nocardia", "Cryptococcus", and "Listeria monocytogenes"

- Transplantation—"Aspergillus", "Candida", "Cryptococcus", "Mucorales", "Nocardia", and "T. gondii"

- Neutropenia—Aerobic gram-negative bacilli, "Aspergillus", "Candida", and "Mucorales"

Severe pain in perimastoid region, difficulty of swallowing, sore throat, difficulty in breathing, nuchal rigidity, and fever.

Bezold's Abscess is an abscess deep to sternocleidomastoid muscle where pus from mastoiditis erodes through the cortex of Mastoid part of the temporal bone, medial to the attachment of sternocleidomastoid, extends into the infratemporal fossa, and deep to the investing layer of the deep cervical fascia . It is a rare complication of acute otitis media.

Anaerobic and microaerophilic cocci and gram-negative and gram-positive anaerobic bacilli are the predominate bacterial isolates. Many brain abscesses are polymicrobical. The predominant organisms include: "Staphylococcus aureus", aerobic and anaerobic streptococci (especially "Streptococcus intermedius"), "Bacteroides", "Prevotella", and "Fusobacterium" species, Enterobacteriaceae, "Pseudomonas" species, and other anaerobes. Less common organisms include: "Haemophillus influenzae", "Streptococcus pneumoniae" and "Neisseria meningitides".

Bacterial abscesses rarely (if ever) arise "de novo" within the brain, although establishing a cause can be difficult in many cases. There is almost always a primary lesion elsewhere in the body that must be sought assiduously, because failure to treat the primary lesion will result in relapse. In cases of trauma, for example in compound skull fractures where fragments of bone are pushed into the substance of the brain, the cause of the abscess is obvious. Similarly, bullets and other foreign bodies may become sources of infection if left in place. The location of the primary lesion may be suggested by the location of the abscess: infections of the middle ear result in lesions in the middle and posterior cranial fossae; congenital heart disease with right-to-left shunts often result in abscesses in the distribution of the middle cerebral artery; and infection of the frontal and ethmoid sinuses usually results in collection in the subdural sinuses.

Sinusitis is inflammation of the paranasal air sinuses. Infections associated with teeth may be responsible for approximately 20% of cases of maxillary sinusitis. The cause of this situation is usually a periapical or periodontal infection of a maxillary posterior tooth, where the inflammatory exudate has eroded through the bone superiorly to drain into the maxillary sinus. Once an odontogenic infection involves the maxillary sinus, it is possible that it may then spread to the orbit or to the ethmoid sinus.

Abscesses are caused by a high-density infection of (usually) common bacteria which collect in one place or another for any variety of reasons. Anal abscesses, without treatment, are likely to spread and affect other parts of the body, particularly the groin and rectal lumen. All abscesses can progress to serious generalized infections requiring lengthy hospitalizations if not treated.

Historically, many rectal abscesses are caused by bacteria common in the digestive system, such as E. coli. While this still continues often to be the case, there has recently been an uptick in the causative organism being staphylococcus, as well as the difficult to treat community-acquired methicillin-resistant S. aureus. Because of the increasing appearance of more exotic bacteria in anal abscesses, microbiological examination will always be performed on the surgical exudate to determine the proper course of any antibiotic treatment.

It is a commonly encountered otorhinolaryngological (ENT) emergency.

The number of new cases per year of peritonsillar abscess in the United States has been estimated approximately at 30 cases per 100,000 people. In a study in Northern Ireland, the number of new cases was 10 cases per 100,000 people per year.

In Denmark, the new number of new cases is higher and reaches 41 cases per 100,000 people per year. Younger children who develop a peritonsillar abscess are often immunocompromised and in them, the infection can cause airway obstruction.

An odontogenic infection is an infection that originates within a tooth or in the closely surrounding tissues. The term is derived from "" (from ancient Greek "odous" - "tooth") and "" (from Greek "genos" - "birth"). Odontogenic infections may remain localized to the region where they started, or spread into adjacent or distant areas.

It is estimated that 90-95% of all orofacial infections originate from the teeth or their supporting structures. Furthermore, about 70% of odontogenic infections occur as periapical inflammation, i.e. acute periapical periodontitis or a periapical abscess. The next most common form of odontogenic infection is the periodontal abscess.

The elderly and those with a weakened immune system are especially vulnerable to contracting cellulitis. Diabetics are more susceptible to cellulitis than the general population because of impairment of the immune system; they are especially prone to cellulitis in the feet, because the disease causes impairment of blood circulation in the legs, leading to diabetic foot or foot ulcers. Poor control of blood glucose levels allows bacteria to grow more rapidly in the affected tissue, and facilitates rapid progression if the infection enters the bloodstream. Neural degeneration in diabetes means these ulcers may not be painful, thus often become infected. Those who have suffered poliomyelitis are also prone because of circulatory problems, especially in the legs.

Immunosuppressive drugs, and other illnesses or infections that weaken the immune system, are also factors that make infection more likely. Chickenpox and shingles often result in blisters that break open, providing a gap in the skin through which bacteria can enter. Lymphedema, which causes swelling on the arms and/or legs, can also put an individual at risk.

Diseases that affect blood circulation in the legs and feet, such as chronic venous insufficiency and varicose veins, are also risk factors for cellulitis.

Cellulitis is also common among dense populations sharing hygiene facilities and common living quarters, such as military installations, college dormitories, nursing homes, oil platforms, and homeless shelters.

Spinal epidural abscess (SEA) is a collection of pus or inflammatory granulation between the dura mater and the vertebral column. Currently the annual incidence rate of SEAs is estimated to be 2.5-3 per 10,000 hospital admissions. Incidence of SEA is on the rise, due to factors such as an aging population, increase in use of invasive spinal instrumentation, growing number of patients with risk factors such as diabetes and intravenous drug use. SEAs are more common in posterior than anterior areas, and the most common location is the thoracolumbar area, where epidural space is larger and contains more fat tissue.

SEAs are more common in males, and can occur in all ages, although highest prevalence is during the fifth and seventh decades of life.

If left untreated, an anal fistula will almost certainly form, connecting the rectum to the skin. This requires more intensive surgery. Furthermore, any untreated abscess may (and most likely will) continue to expand, eventually becoming a serious systemic infection.

An epidural abscess refers to a collection of pus and infectious material located in the epidural space of the central nervous system. Due to its location adjacent to brain or spinal cord, epidural abscesses have the potential to cause weakness, pain, and paralysis.

The bacteria causing the thrombophlebitis are anaerobic bacteria that are typically normal components of the microorganisms that inhabit the mouth and throat. Species of "Fusobacterium", specifically "Fusobacterium necrophorum", are most commonly the causative bacteria, but various bacteria have been implicated. One 1989 study found that 81% of Lemierres's syndrome had been infected with "Fusobacterium necrophorum", while 11% were caused by other Fusobacterium species. MRSA might also be an issue in Lemierre infections. Rarely Lemierre's syndrome is caused by other (usually Gram-negative) bacteria, which include "Bacteroides fragilis" and "Bacteroides melaninogenicus", "Peptostreptococcus spp.", "Streptococcus microaerophile", "Staphylococcus aureus", "Streptococcus pyogenes", and "Eikenella corrodens".

If left untreated, a severe tooth abscess may become large enough to perforate bone and extend into the soft tissue eventually becoming osteomyelitis and cellulitis respectively. From there it follows the path of least resistance and may spread either internally or externally. The path of the infection is influenced by such things as the location of the infected tooth and the thickness of the bone, muscle and fascia attachments.

External drainage may begin as a boil which bursts allowing pus drainage from the abscess, intraorally (usually through the gum) or extraorally. Chronic drainage will allow an epithelial lining to form in this communication to form a pus draining canal (fistula). Sometimes this type of drainage will immediately relieve some of the painful symptoms associated with the pressure.

Internal drainage is of more concern as growing infection makes space within the tissues surrounding the infection. Severe complications requiring immediate hospitalization include Ludwig's angina, which is a combination of growing infection and cellulitis which closes the airway space causing suffocation in extreme cases. Also infection can spread down the tissue spaces to the mediastinum which has significant consequences on the vital organs such as the heart. Another complication, usually from upper teeth, is a risk of septicaemia (infection of the blood) from connecting into blood vessels, brain abscess (extremely rare), or meningitis (also rare).

Depending on the severity of the infection, the sufferer may feel only mildly ill, or may in extreme cases require hospital care.

When properly diagnosed, the mortality of Lemierre's syndrome is about 4.6%. Since this disease is not well known and often remains undiagnosed, mortality might be much higher.