The third and final stage, and hallmark of EGPA, is inflammation of the blood vessels, and the consequent reduction of blood flow to various organs and tissues. Local and systemic symptoms become more widespread and are compounded by new symptoms from the vasculitis.

Severe complications may arise. Blood clots may develop within the damaged arteries in severe cases, particularly in arteries of the abdominal region, which is followed by infarction and cell death, or slow atrophy. Many patients experience severe abdominal complaints; these are most often due to peritonitis and/or ulcerations and perforations of the gastrointestinal tract, but occasionally due to acalculous cholecystitis or granulomatous appendicitis.

The most serious complication of the vasculitic stage is heart disease, which is the cause of nearly one-half of all deaths in patients with EGPA. Among heart disease-related deaths, the most usual cause is inflammation of the heart muscle caused by the high level of eosinophils, although some are deaths due to inflammation of the arteries that supply blood to the heart or pericardial tamponade. Kidney complications have been reported as being less common.

Eosinophilic granulomatosis with polyangiitis consists of three stages, but not all patients develop all three stages or progress from one stage to the next in the same order; whereas some patients may develop severe or life-threatening complications such as gastrointestinal involvement and heart disease, some patients are only mildly affected, "e.g." with skin lesions and nasal polyps. EGPA is consequently considered a highly variable condition in terms of its presentation and its course.

Eosinophilia can be idiopathic (primary) or, more commonly, secondary to another disease. In the Western World, allergic or atopic diseases are the most common causes, especially those of the respiratory or integumentary systems. In the developing world, parasites are the most common cause. A parasitic infection of nearly any bodily tissue can cause eosinophilia.

Diseases that feature eosinophilia as a sign include:

- Allergic disorders

- Asthma

- Hay fever

- Drug allergies

- Allergic skin diseases

- Pemphigus

- Dermatitis herpetiformis

- IgG4-related disease

- Parasitic infections

- Addison's disease and stress-induced suppression of adrenal gland function

- Some forms of malignancy

- Acute lymphoblastic leukemia

- Chronic myelogenous leukemia

- Eosinophilic leukemia

- Clonal eosinophilia

- Hodgkin lymphoma

- Some forms of non-Hodgkin lymphoma

- Lymphocyte-variant hypereosinophilia

- Systemic mastocytosis

- Systemic autoimmune diseases

- Systemic lupus erythematosus

- Kimura disease

- Eosinophilic granulomatosis with polyangiitis

- Eosinophilic fasciitis

- Eosinophilic myositis

- Eosinophilic esophagitis

- Eosinophilic gastroenteritis

- Cholesterol embolism (transiently)

- Coccidioidomycosis (Valley fever), a fungal disease prominent in the US Southwest.

- Human immunodeficiency virus infection

- Interstitial nephropathy

- Hyperimmunoglobulin E syndrome, an immune disorder characterized by high levels of serum IgE

- Idiopathic hypereosinophilic syndrome.

- Congenital disorders

- Hyperimmunoglobulin E syndrome

- Omenn syndrome

- Familial eosinophilia

In adults, the prevalence of IgE sensitization to allergens from house dust mite and cat, but not grass, seem to decrease over time as people age. However, the biological reasons for these changes are not fully understood.

Allergic reactions to drugs are a common cause of eosinophilia, with manifestations ranging from diffuse maculopapular rash, to severe life-threatening drug reactions with eosinophilia and systemic symptoms (DRESS). Drugs that have been shown to cause DRESS are aromatic anticonvulsants and other antiepileptics, sulfonamides, allopurinol, nonsteroidal anti-inflammatory drugs (NSAIDs), some antipsychotics such as risperidone, and certain antibiotics. Phenibut, an analogue of the neurotransmitter GABA, has also been implicated in high doses. The reaction which has been shown to be T-cell mediated may also cause eosinophilia-myalgia syndrome.

The following are causes of BHL:

- Sarcoidosis

- Infection

- Tuberculosis

- Fungal infection

- Mycoplasma

- Intestinal Lipodystrophy (Whipple's disease)

- Malignancy

- Lymphoma

- Carcinoma

- Mediastinal tumors

- Inorganic dust disease

- Silicosis

- Berylliosis

- Extrinsic allergic alveolitis

- Such as bird fancier's lung

- Less common causes also exist:

- Eosinophilic granulomatosis with polyangiitis

- Human immunodeficiency virus

- Extrinsic allergic alveolitis

- Adult-onset Still's disease

There is a strong genetic predisposition toward atopic allergies, especially on the maternal side. Because of the strong familial evidence, investigators have tried to map susceptibility genes for atopy. Genes for atopy (C11orf30, STAT6, SLC25A46, HLA-DQB1, IL1RL1/IL18R1, TLR1/TLR6/TLR10, LPP, MYC/PVT1, IL2/ADAD1, HLA-B/MICA) tend to be involved in allergic responses or other components of the immune system. C11orf30 seems to be the most relevant for atopy as it may increase susceptibility to poly-sensitization.

With no particular affinity to any particular ethnic group, seen in all age groups and equally amongst males and females, the precise prevalence is not known.

Chronic stress can aggravate allergic conditions. This has been attributed to a T helper 2 (TH2)-predominant response driven by suppression of interleukin 12 by both the autonomic nervous system and the hypothalamic–pituitary–adrenal axis. Stress management in highly susceptible individuals may improve symptoms.

Allergic conjunctivitis occurs more frequently among those with allergic conditions, with the symptoms having a seasonal correlation.

Allergic conjunctivitis is a frequent condition as it is estimated to affect 20 percent of the population on an annual basis and approximately one-half of these people have a personal or family history of atopy.

Giant papillary conjunctivitis accounts for 0.5–1.0% of eye disease in most countries.

The Allergic Alсоhоl from the original on 30 April 2012. Retrieved 2010-04-08.

The cause of allergic conjunctivitis is an allergic reaction of the body's immune system to an allergen. Allergic conjunctivitis is common in people who have other signs of allergic disease such as hay fever, asthma and eczema.

Among the most common allergens that cause conjunctivitis are:

- Pollen from trees, grass and ragweed

- Animal skin and secretions such as saliva

- Perfumes

- Cosmetics

- Skin medicines

- Air pollution

- Smoke

- Dust mites

- Balsam of Peru (used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties)

- Eye drops

Most cases of seasonal conjunctivitis are due to pollen and occur in the hay fever season, grass pollens in early summer and various other pollens and moulds may cause symptoms later in the summer.

EoE is a relatively poorly understood disease of which awareness is rising.

At a tissue level, EoE is characterized by a dense infiltrate with white blood cells of the eosinophil type into the epithelial lining of the esophagus. This is thought to be an allergic reaction against ingested food, based on the important role eosinophils play in allergic reactions. Eosinophils are inflammatory cells that release a variety of chemical signals which inflame the surrounding esophageal tissue. This results in the signs and symptoms of pain, visible redness on endoscopy, and a natural history that may include stricturing.

Urticarial allergic eruption is a cutaneous condition characterized by annular or gyrate urticarial plaques that persist for greater than 24 hours.

Although genetic factors govern susceptibility to atopic disease, increases in atopy have occurred within too short a time frame to be explained by a genetic change in the population, thus pointing to environmental or lifestyle changes. Several hypotheses have been identified to explain this increased rate; increased exposure to perennial allergens due to housing changes and increasing time spent indoors, and changes in cleanliness or hygiene that have resulted in the decreased activation of a common immune control mechanism, coupled with dietary changes, obesity and decline in physical exercise. The hygiene hypothesis maintains that high living standards and hygienic conditions exposes children to fewer infections. It is thought that reduced bacterial and viral infections early in life direct the maturing immune system away from T1 type responses, leading to unrestrained T2 responses that allow for an increase in allergy.

Changes in rates and types of infection alone however, have been unable to explain the observed increase in allergic disease, and recent evidence has focused attention on the importance of the gastrointestinal microbial environment. Evidence has shown that exposure to food and fecal-oral pathogens, such as hepatitis A, "Toxoplasma gondii", and "Helicobacter pylori" (which also tend to be more prevalent in developing countries), can reduce the overall risk of atopy by more than 60%, and an increased rate of parasitic infections has been associated with a decreased prevalence of asthma. It is speculated that these infections exert their effect by critically altering T1/T2 regulation. Important elements of newer hygiene hypotheses also include exposure to endotoxins, exposure to pets and growing up on a farm.

Some examples:

- Allergic asthma

- Allergic conjunctivitis

- Allergic rhinitis ("hay fever")

- Anaphylaxis

- Angioedema

- Urticaria (hives)

- Eosinophilia

- Penicillin allergy

- Cephalosporin allergy

- Food allergy

- Sweet itch

Plasma cell gingivits is rare, and plasma cell cheilitis is very rare. Most people with plasma cell cheilitis have been elderly.

There is no good evidence that a mother's diet during pregnancy, the formula used, or breastfeeding changes the risk. There is tentative evidence that probiotics in infancy may reduce rates but it is insufficient to recommend its use.

People with eczema should not get the smallpox vaccination due to risk of developing eczema vaccinatum, a potentially severe and sometimes fatal complication.

Causes include infection with dermatophytosis, Mycobacterium, viruses, bacteria and parasites. Eczematous conditions including contact allergic dermatitis and stasis dermatitis as well as stitches and trauma have also been associated with id reactions. Radiation treatment of tinea capitis has been reported as triggering an id reaction.

In acquired angioedema, HAE types I and II, and nonhistaminergic angioedema, antifibrinolytics such as tranexamic acid or ε-aminocaproic acid may be effective. Cinnarizine may also be useful because it blocks the activation of C4 and can be used in patients with liver disease, while androgens cannot.

This is a rare inflammatory condition of the minor salivary glands, usually in the lower lip, which appears swollen and everted. There may also be ulceration, crusting, abscesses, and sinus tracts. It is an acquired disorder, but the cause is uncertain. Suspected causes include sunlight, tobacco, syphilis, poor oral hygiene and genetic factors. The openings of the minor salivary gland ducts become inflamed and dilated, and there may be mucopurulent discharge from the ducts. A previous classification suggested dividing cheilitis into 3 types based on severity, with the later stages involving secondary infection with bacteria, and increased ulceration, suppuration and swelling: Type 1, Simple; Type 2, Superficial suppurative ("Baelz's disease"); and Type 3, Deep suppurative ("cheilitis glandularis epostemetosa"). Cheilitis glandularis usually occurs in middle-aged and elderly males, and it carries a risk of malignant transformation to squamous cell carcinoma (18% to 35%). Preventative treatment such as vermilionectomy ("lip shave") is therefore the treatment of choice.

Eosinophilic esophagitis (EoE, also spelled eosinophilic oesophagitis), also known as allergic oesophagitis, is an allergic inflammatory condition of the esophagus that involves eosinophils, a type of white blood cell. Symptoms are swallowing difficulty, food impaction, vomiting, and heartburn.

Eosinophilic esophagitis was first described in children but also occurs in adults. The condition is not well understood, but food allergy may play a significant role. The treatment may consist of removal of known or suspected triggers and medication to suppress the immune response. In severe cases, it may be necessary to stretch the esophagus with an endoscopy procedure.

The disorder is thought to be caused by an anomaly in the arachidonic acid metabolizing cascade which leads to increased production of pro-inflammatory cysteinyl leukotrienes, a series of chemicals involved in the body's inflammatory response. When medications like NSAIDs or aspirin block the COX-1 enzyme, production of thromboxane and some anti-inflammatory prostaglandins is decreased, and in patients with aspirin-induced asthma this results in the overproduction of pro-inflammatory leukotrienes to causes severe exacerbations of asthma and allergy-like symptoms. The underlying cause of the disorder is not fully understood, but there have been several important findings:

- Abnormally low levels of prostaglandin E (PGE), which is protective for the lungs, has been found in patients with aspirin-induced asthma and may worsen their lung inflammation.

- In addition to the overproduction of cystinyl leukotrienes, overproduction of 15-lipoxygenase-derived arachidonic acid metabolites viz., 15-hydroxyicosatetraenoic acid and eoxins by the eosinophils isolated from the blood of individuals with AERD; certain of these products may help promote the inflammatory response.

- Overexpression of both the cysteinyl leukotriene receptor 1 and the leukotriene C synthase enzyme has been shown in respiratory tissue from patients with aspirin-induced asthma, which likely relates to the increased response to leukotrienes and increased production of leukotrienes seen in the disorder.

- The attachment of platelets to certain leukocytes in the blood of patients with aspirin-sensitive asthma has also been shown to contribute to the overproduction of leukotrienes.

- There may be a relationship between aspirin-induced asthma and "TBX21", "PTGER2", and "LTC4S".

- Eosinophils isolated from the blood of aspirin-induced asthma subjects (as well as severe asthmatic patients) greatly overproduce 15-hydroxyicosatetraenoic acid and eoxin C4 when challenged with arachidonic acid or calcium ionophore A23187, compared to the eosinophils taken from normal or mildly asthmatic subjects; aspirin treatment of eosinophils from aspirin intolerant subjects causes the cells to mount a further increase in eoxin production. These results suggest that 15-lipoxygenase and certain of its metabolites, perhaps eoxin C4, as contributing to aspirin-induced asthma in a fashion similar to 5-lipoxygenase and its leukotriene metabolites.

Malnutrition (improper dietary intake) or malabsorption (poor absorption of nutrients into the body) can lead to nutritional deficiency states, several of which can lead to stomatitis. For example, deficiencies of iron, vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B6 (pyridoxine), vitamin B9 (folic acid) or vitamin B12 (cobalamine) may all manifest as stomatitis. Iron is necessary for the upregulation of transcriptional elements for cell replication and repair. Lack of iron can cause genetic downregulation of these elements, leading to ineffective repair and regeneration of epithelial cells, especially in the mouth and lips. Many disorders which cause malabsorption can cause deficiencies, which in turn causes stomatitis. Examples include tropical sprue.

Samter's triad goes by several other names:

A sufferer who has not yet experienced asthma or aspirin sensitivity might be diagnosed as having:

- Non-allergic rhinitis

- Non-allergic rhinitis with eosinophilia syndrome (NARES)

Allergic contact stomatitis (also termed "allergic gingivostomatitis" or "allergic contact gingivostomatitis") is a type IV (delayed) hypersensitivity reaction that occurs in susceptible atopic individuals when allergens penetrate the skin or mucosa.

Allergens, which may be different for different individuals, combine with epithelial-derived proteins, forming haptens which bind with Langerhans cells in the mucosa, which in turn present the antigen on their surface to T lymphocytes, sensitizing them to that antigen and causing them to produce many specific clones. The second time that specific antigen is encountered, an inflammatory reaction is triggered at the site of exposure. Allergic contact stomatitis is less common than allergic contact dermatitis because the mouth is coated in saliva, which washes away antigens and acts as a barrier. The oral mucosa is also more vascular (has a better blood supply) than skin, meaning that any antigens are more quickly removed from the area by the circulation. Finally, there is substantially less keratin in oral mucosa, meaning that there is less likelihood that haptens will form.

Allergic contact stomatitis appears as non-specific inflammation, so it may be mistaken for chronic physical irritation. There may be burning or soreness of the mouth and ulceration. Chronic exposure to the allergen may result in a lichenoid lesion. Plasma cell gingivitis may also occur, which may be accompanied by glossitis and cheilitis.

Allergens that may cause allergic contact stomatitis in some individuals include cinnamaldehyde, Balsam of Peru, peppermint, mercury, gold, pyrophosphates, zinc citrate, free acrylic monomer, nickel, fluoride, and sodium lauryl sulfate. These allergens may originate from many sources, including various foods and drink, chewing gum, toothpaste, mouthwash, dental floss, dental fillings, dentures, orthodontic bands or wires, and many other sources. If the substance containing the allergen comes into contact with the lips, allergic contact cheilitis can occur, together with allergic contact stomatitis.

The diagnosis is confirmed by patch test, and management is by avoidance of exposure to the allergen.