air to escape from both the nose and the mouth. Nasal airflow is also used to produce a variety of click consonants called nasal clicks. The large, hollow cavities of the paranasal sinuses act as resonating chambers that modify, and amplify speech and other vocal vibrations passing through them. Clinical significance One of the most common medical conditions involving the nose is a nosebleed (epistaxis). Most nosebleeds occur in Kiesselbach's plexus, a vascular plexus in the lower front part of the septum involving the convergence of four arteries. A smaller proportion of nosebleeds that tend to be nontraumatic occur in Woodruff's plexus. Woodruff's plexus is a venous plexus of large thin-walled veins lying in the posterior part of the inferior meatus. Another common condition is nasal congestion, usually a symptom of infection, particularly sinusitis, or other inflammation of the nasal lining called rhinitis, including allergic rhinitis and nonallergic rhinitis. Chronic nasal obstruction resulting in breathing through the mouth can greatly impair or prevent the nostrils from flaring. One of the causes of snoring is nasal obstruction, and anti-snoring devices such as a nasal strip help to flare the nostrils and keep the airway open. Nasal flaring, is usually seen in children when breathing is difficult. Most conditions of nasal congestion also cause a loss of the sense of smell (anosmia). This may also occur in other conditions, for example following trauma, in Kallmann syndrome or Parkinson's disease. A blocked sinus ostium, an opening from a paranasal sinus, will cause fluid to accumulate in the sinus. In children the nose is a common site of foreign bodies. The nose is one of the exposed areas that is susceptible to frostbite. Because of the special nature of the blood supply to the human nose and surrounding area, it is possible for retrograde infections from the nasal area to spread to the brain. For this reason, the area from the corners of the mouth to the bridge of the nose, including the nose and maxilla, is known as the danger triangle of the face. Infections or other conditions that may result in destruction of, or damage to a part of the nose include rhinophyma, skin cancers particularly basal-cell carcinoma, paranasal sinus and nasal cavity cancer, granulomatosis with polyangiitis, syphilis, leprosy, recreational use of cocaine, chromium and other toxins. The nose may be stimulated to grow in acromegaly, a condition caused by an excess