Orbital cellulitis can complicate acute ethmoiditis if anterior and posterior ethmoidal veins thrombophlebitis enables the spread of the infection to the lateral or orbital side of the ethmoid labyrinth. Sinusitis may extend to the central nervous system, where it may cause cavernous sinus thrombosis, retrograde meningitis, and epidural, subdural, and brain abscesses. Orbital symptoms frequently precede intracranial spread of the infection . Other complications include sinobronchitis, maxillary osteomyelitis, and frontal bone osteomyelitis. Osteomyelitis of the frontal bone often originates from a spreading thrombophlebitis. A periostitis of the frontal sinus causes an osteitis and a periostitis of the outer membrane, which produces a tender, puffy swelling of the forehead.The diagnosis of these complications can be assisted by noting local tenderness and dull pain, and can be confirmed by CT and nuclear isotope scanning. The most common microbial causes are anaerobic bacteria and S. aureus. Treatment includes performing surgical drainage and administration of antimicrobial therapy. Surgical debridement is rarely required after an extended course of parenteral antimicrobial therapy. Chronic sinus infections may lead to mouth breathing, which can result in mouth dryness and an increased risk of gingivitis. Decongestants may also cause mouth dryness.If an odontogenic infection involves the maxillary sinus, odontogenic sinusitis (ODS) may ensue. Odontogenic sinusitis can often spread to other sinuses such as the ethmoid, frontal and (less frequently) sphenoid sinus, and even to the contralateral nasal cavity.
Digestive tract
Causes in the digestive tract

Gastritis (inflammation of the gastric wall)
Gastroenteritis
Gastroesophageal reflux disease
Celiac disease
Non-celiac gluten sensitivity
Pyloric stenosis (in babies, this typically causes a very forceful "projectile vomiting" and is an indication for urgent surgery)
Bowel obstruction
Overeating (stomach too full)
Acute abdomen and/or peritonitis
Ileus
Food allergies (often in conjunction with hives or swelling)
Cholecystitis, pancreatitis, appendicitis, hepatitis
Food poisoning
In children, it can be caused by an allergic reaction to cows milk proteins (Milk allergy or lactose intolerance)

Sensory system and brain
Causes in the sensory system:
Movement leading to motion sickness (which is caused by overstimulation of the labyrinthine canals of the ear)
Ménières disease
VertigoCauses in the brain:
Concussion
Cerebral hemorrhage
Migraine
Brain tumors, which can cause the chemoreceptors to malfunction
Benign intracranial hypertension and hydrocephalusMetabolic disturbances (these may irritate both the stomach and the parts of the brain that coordinate vomiting):
Hypercalcemia (high calcium levels)
Uremia (urea accumulation, usually due to kidney failure)
Adrenal insufficiency
Hypoglycemia
HyperglycemiaPregnancy:
Hyperemesis, morning sicknessDrug reaction (vomiting may occur as an acute somatic response to):
Alcohol, which can be partially oxidized into acetaldehyde that causes the symptoms of hangover, including nausea, vomiting, shortness of breath, and fast heart rate. Opioids
Selective serotonin reuptake inhibitors
Many chemotherapy drugs
Some entheogens (such as peyote or ayahuasca)Illness (sometimes colloquially known as "stomach flu"—a broad name that refers to gastric inflammation caused by a range of viruses and bacteria):
Norovirus (formerly Norwalk virus or Norwalk agent)
Swine influenzaPsychiatric/behavioral:

Bulimia nervosa
Purging disorder

Emetics
An emetic, such as syrup of ipecac, is a substance that induces vomiting when administered orally or by injection. An emetic is used medically when a substance has been ingested and must be expelled from the body immediately.