Drugs that commonly induce DRESS syndrome include phenobarbital, carbamazepine, phenytoin, lamotrigine, minocycline, sulfonamides, allopurinol, modafinil, dapsone, ziprasidone, vancomycin, and most recently olanzapine.

It has been associated with HHV-6 reactivation.

Drug reaction with eosinophilia and systemic symptoms (DRESS syndrome) is caused by exposure to certain medications that may result in a rash, fever, inflammation of internal organs, lymphadenopathy, and characteristic hematologic abnormalities such as eosinophilia, thrombocytopenia, and atypical lymphocytosis. The syndrome has about a 10% mortality. Treatment consists of stopping the offending medication and providing supportive care. Systemic steroids are commonly used, as well, but no controlled clinical trials assess the efficacy of this treatment.

The term was coined in a 1996 report in an attempt to simplify terminology for a syndrome recognized as early as 1959.

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

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.

NSAID or nonsteroidal anti-inflammatory drug hypersensitivity reactions encompasses a broad range of allergic or allergic-like symptoms that occur within minutes to hours after ingesting aspirin or other NSAID nonsteroidal anti-inflammatory drugs. Hypersensitivity drug reactions differ from drug toxicity reactions in that drug toxicity reactions result from the pharmacological action of a drug, are dose-related, and can occur in any treated individual (see nonsteroidal anti-inflammatory drugs section on adverse reactions for NSAID-induced toxic reactions); hypersensitivity reactions are idiosyncratic reactions to a drug. Although the term NSAID was introduced to signal a comparatively low risk of adverse effects, NSAIDs do evoke a broad range of hypersensitivity syndromes. These syndromes have recently been classified by the European Academy of Allergy and Clinical Immunology Task Force on NSAIDs Hypersensitivity. The classification organizes the hypersensitivity reactions to NSAIDs into the following five categories:

- 1) NSAIDs-exacerbated respiratory disease (NERD) is an acute (immediate to several hours) exacerbation of bronchoconstriction and other symptoms of asthma (see aspirin-induced asthma) in individuals with a history of asthma and/or nasal congestion, rhinorrhea or other symptoms of rhinitis and sinusitis in individuals with a history of rhinosinusitis after ingestion of various NSAIDs, particularly those that act by inhibiting the COX-1 enzyme. NERD does not appear to be due to a true allergic reaction to NSAIDs but rather at least in part to the more direct effects of these drugs to promote the production and/or release of certain mediators of allergy. That is, inhibition of cellular COX activity deprives tissues of its anti-inflammatory product(s), particularly prostaglandin E2 while concurrently shuttling its substrate, arachidonic acid, into other metabolizing enzymes, particularly 5-lipoxygenase (ALOX5) to overproduce pro-inflammatory leukotriene and 5-Hydroxyicosatetraenoic acid metabolites and 15-lipoxygenase (ALOX15) to overproduce pro-inflammatory 15-Hydroxyicosatetraenoic acid metabolites, including eoxins; the condition is also associated with a reduction in the anti-inflammatory metabolite, lipoxin A4, and increases in certain pro-allergic chemokines such as eotaxin-2 and CCL7.

- 2) NSAIDs-exacerbated cutaneous disease (NECD) is an acute exacerbation of wheals and/or angioedema in individuals with a history of chronic urticaria. NECD also appears due to the non-allergic action of NSAIDs in inhibiting the production of COX anti-inflammatory metabolites while promoting the production 5-lipoxygenase and 15-lipoxygenase pro-inflammatory metabolites and the overproduction of certain pro-allergic chemokines, e.g. eotaxin-1, eotaxin-2, RANTES, and interleukin-5.

- 3) NSAIDs-induced urticarial disease (NEUD) is the acute development of wheals and/or angioedema in individuals with no history of chronic NSAIDs-induced urticaria or related diseases. The mechanism behind NEUD is unknown but may be due to the non-allergic action of NSAIDs in promoting the production and/or release of allergy mediators.

- 4) Single NSAID-induced urticarial/angioedema or anaphylaxis (SNIUAA) is the acute development of urticarial, angioedema, or anaphylaxis in response to a single type of NSAID and/or a single group of NSAIDs with a similar structure but not to other structurally unrelated NSAIDs in individuals with no history of underlying relevant chronic diseases. SNIUAA is due to a true IgE-mediated allergy reaction.

- 5 Single NSAID-induced delayed reactions (SNIDR) are a set of delayed onset (usually more than 24 hour) reactions to NSAIDs. SNIDR are most commonly skin reactions that may be relatively mild moderately severe such as maculopapular rash, fixed drug eruptions, photosensitivity reactions, delayed urticaria, and contact dermatitis or extremely severe such as the DRESS syndrome, acute generalized exanthematous pustulosis, the Stevens–Johnson syndrome, and toxic epidermal necrolysis (also termed Lyell's syndrome). SNIDR result from the drug-specific stimulation of CD4+ T lymphocytes and CD8+ cytotoxic T cells to elicit a delayed type hypersensitivity reaction.

Hypereosiophilia or eosinophilia may be associated with the following autoimmune diseases: systemic lupus erythematosus eosinophilic fasciitis, eosinophilic granulomatosis with polyangiitis, dermatomyositis, severe rheumatoid arthritis, progressive systemic sclerosis, Sjogren syndrome, thromboangiitis obliterans, Behcet syndrome, IgG4-related disease, inflammatory bowel diseases, sarcoidosis, bullous pemphigoid, and dermatitis herpetiformis.

Helminths are common causes of hypereosiophilia and eosinophilia in areas endemic to these parasites. Helminths infections causing increased blood eosinophil counts include: 1) nematodes, (i.e. "Angiostrongylus cantonensis" and Hookworm infections), ascariasis, strongyloidiasis trichinosis, visceral larva migrans, Gnathostomiasis, cysticercosis, and echinococcosis; 2) filarioidea, i.e. tropical pulmonary eosinophilia, loiasis, and onchocerciasis; and 3) flukes, i.e. shistosomiasis, fascioliasis, clonorchiasis, paragonimiasis, and fasciolopsiasis. Other infections associated with increased eosinophil blood counts include: protozoan infections, i.e. "Isospora belli" and "Dientamoeba fragilis") and sarcocystis); fungal infections (i.e. disseminated histoplasmosis, cryptococcosis especially in cases with [[central nervous system]] involvement), and coccidioides); and viral infections, i.e. Human T-lymphotropic virus 1 and HIV.

There are many causes of eosinophilia that may underlie eosinophilic myocarditis. These causes are classified as primary (i.e. a defect intrinsic to the eosinophil cell line), secondary (induced by an underlying disorder that stimulates the proliferation and activation of eosinophils), or idiopathic (i.e. unknown cause). Non-idiopathic causes of the disorder are sub-classified into various forms of allergic, autoimmune, infectious, or malignant diseases and hypersensitivity reactions to drugs, vaccines, or transplanted hearts. While virtually any cause for the elevation and activation of blood eosinophils must be considered as a potential cause for eosinophilic myocarditis, the follow list gives the principal types of eosinophilia known or thought to underlie the disorder.

Primary conditions that may lead to eosinophilic myocarditis are:

- Clonal hypereosinophilia.

- Chronic eosinophilic leukemia.

- The idiopathic hypereosinophilic syndrome.

Secondary conditions that may lead to eosinophilic myocarditis are:

- Infections agents:

- Parasitic worms: various "Ascaris, Strongyloides, Schistosoma, filaria, Trematoda", and "Nematode" species. Parasitic infestations often cause significant heart valve disease along with myocarditis and the disorder in this setting is sometimes termed Tropical endomyocardial fibrosis. While commonly considered to be due to the cited parasites, this particular form of eosinophilic myocarditis may more often develop in individuals with other disorders, e.g. malnutrition, dietary toxins, and genetic predisposition, in addition to or place of round worm infestation.

- Infections by protozoa: various "Toxoplasma gondii, Trypanosoma cruzi, trichinella spiralis, Entamoeba", and "Echinococcus" species.

- Viruses: While some viral infections (e.g. HIV) have been considered causes of eosinophilic endocarditis, a study of 20 patients concluded that viral myocarditis lacks the characteristic of eosinophil-induced damage in hearts taken during cardiac transplantation.

- Allergic and autoimmune diseases such as severe asthma, rhinitis, or urticarial, chronic sinusitis, aspirin-induced asthma, allergic bronchopulmonary aspergillosis, chronic eosinophilic pneumonia, Kimura's disease, polyarteritis nodosa, eosinophilic granulomatosis with polyangiitis (i.e. Churg-Strauss syndrome), and rejection of transplanted hearts.

- Malignancies and/or premalignant hematologic conditions not due to a primary disorder in eosinophils such as Gleich's syndrome, Lymphocyte-variant hypereosinophilia Hodgkin disease, certain T-cell lymphomas, acute myeloid leukemia, the myelodysplastic syndromes, systemic mastocytosis, chronic myeloid leukemia, polycythemia vera, essential thrombocythemia, myelofibrosis, chronic myelomonocytic leukemia, and T-lymphoblastic leukemia/lymphoma-associated or myelodysplastic–myeloproliferative syndrome-associated eosinophilias; IgG4-related disease and Angiolymphoid hyperplasia with eosinophilia as well as non-hematologic cancers such as solid tumors of the lung, gastrointestinal tract, and genitourinary tract.

- Hypersensitivity reactions to agents include:

- Antibiotics/anti-viral agents: various penicillins (e.g. penicillin, ampicillin), cephalosporins (e.g. cephalosporin), tetracyclins (e.g. tetracycline), sulfonamides (e.g. sulfadiazine, sulfafurazole), sulfonylureas, antituburcular drugs (e.g. isoniazid, 4-aminosalicylic acid), linezolid, amphotericin B, chloramphenicol, streptomycin, dapsone, nitrofurantoin, metronidazole, nevirapine, efavirenz, abacavir, nevirapine.

- Anticonvulsants/Antipsychotics/antidepressants: phenindione, phenytoin, phenobarbital, lamotrigine, lamotrigine, clozapine, valproic acid, carbamazepine, desipramine, fluoxetine, amitriptyline, olanzapine.

- Anti-inflammatory agents: ibuprofen, indomethacin, phenylbutazone, oxyphenbutazone, acetazolamide, piroxicam, diclofenac.

- Diuretics: hydrochlorothiazide, spironolactone, chlortalidone.

- ACE inhibitors: captopril, enalapril.

- Other drugs: digoxin, ranitidine, lenalidomide, methyldopa, interleukin 2, dobutamine, acetazolamide.

- Contaminants: Unidentified contaminants inrapeseed oil cause the toxic oil syndrome and in commercial batches of the amino acid, L-tryptophan, cause the eosinophilia–myalgia syndrome.

- Vaccinations: Tetanus toxoid, smallpox, and diphtheria/pertussis/tetanus vaccinations.

The DRESS syndrome is a severe immunological drug reaction. It differs from other drug reactions in that it: a) is caused by a particular set of drugs; b) typically occurs after a delay of 2 to 8 weeks following intake of an offending drug; c) presents with a specific set of signs and symptoms (i.e. modest or extreme elevations in blood eosinophil and atypical lymphocyte counts; acute onset of a skin rash; lymphadenopathy; fever; neuralgia; and involvement of at least one internal organ such as the liver, lung, or heart; d) develops in individuals with particular genetic predispositions; and e) involves reactivation of latent viruses, most commonly human herpesvirus 6 or more rarely human herpes virus 5 (i.e. human cytomegalovirus), human herpesvirus 7, and human herpesvirus 4 (i.e. Epstein–Barr virus). These virus usually become dormant after infecting humans but under special circumstances, such as drug intake, are reactivated and may contribute to serious diseases such as the DRESS syndrome.

Urticaria is a vascular reaction of the skin characterized by the appearance of wheals, which are firm, elevated swelling of the skin. Angioedema, which can occur alone or with

urticaria, is characterized by a well-defined, edematous swelling that involves subcutaneous tissues, abdominal organs, or upper airway.

- Acquired C1 esterase inhibitor deficiency

- Acute urticaria

- Adrenergic urticaria

- Anaphylaxis

- Aquagenic urticaria

- Cholinergic urticaria

- Chronic urticaria (ordinary urticaria)

- Cold urticaria

- Dermatographism (dermographism)

- Episodic angioedema with eosinophilia (Gleich's syndrome)

- Exercise urticaria (exercise-induced urticaria)

- Galvanic urticaria

- Heat urticaria

- Hereditary angioedema (Quincke's edema)

- Localized heat contact urticaria

- Mast cell-independent urticaria

- Physical urticaria

- Primary cold contact urticaria

- Pressure urticaria (delayed pressure urticaria)

- Reflex cold urticaria

- Schnitzler syndrome

- Secondary cold contact urticaria

- Solar urticaria

- Systemic capillary leak syndrome

- Urticarial allergic eruption

- Urticaria-like follicular mucinosis

- Vibratory angioedema

Documented cases of Reye syndrome in adults are rare. The recovery of adults with the syndrome is generally complete, with liver and brain function returning to normal within two weeks of onset. In children, however, mild to severe permanent brain damage is possible, especially in infants. Over thirty percent of the cases reported in the United States from 1981 through 1997 resulted in fatality.

Reye syndrome occurs almost exclusively in children. While a few adult cases have been reported over the years, these cases do not typically show permanent neural or liver damage. Unlike in the UK, the surveillance for Reye syndrome in the US is focused on patients under 18 years of age.

In 1980, after the CDC began cautioning physicians and parents about the association between Reye syndrome and the use of salicylates in children with chickenpox or virus-like illnesses, the incidence of Reye syndrome in the United States began to decline. However, the decline began prior to the FDA's issue of warning labels on aspirin in 1986. In the United States between 1980 and 1997, the number of reported cases of Reye syndrome decreased from 555 cases in 1980 to about 2 cases per year since 1994. During this time period 93% of reported cases for which racial data were available occurred in whites and the median age was six years. In 93% of cases a viral illness had occurred in the preceding three-week period. For the period 1991-1994, the annual rate of hospitalizations due to Reye syndrome in the US was estimated to be between 0.2 and 1.1 per million population less than 18 years of age.

During the 1980s, a case-control study carried out in the United Kingdom also demonstrated an association between Reye syndrome and aspirin exposure. In June 1986, the United Kingdom Committee on Safety of Medicines issued warnings against the use of aspirin in children under 12 years of age and warning labels on aspirin-containing medications were introduced. UK surveillance for Reye syndrome documented a decline in the incidence of the illness after 1986. The reported incidence rate of Reye syndrome decreased from a high of 0.63 per 100,000 population less than 12 years of age in 1983/84 to 0.11 in 1990/91.

From November 1995 to November 1996 in France, a national survey of pediatric departments for children under 15 years of age with unexplained encephalopathy and a threefold (or greater) increase in serum aminotransferase and/or ammonia led to the identification of nine definite cases of Reye syndrome (0.79 cases per million children). Eight of the nine children with Reye syndrome were found to have been exposed to aspirin. In part because of this survey result, the French Medicines Agency reinforced the international attention to the relationship between aspirin and Reye syndrome by issuing its own public and professional warnings about this relationship.

Ionizing radiation-induced cutaneous conditions result from exposure to ionizing radiation.

- Acute radiodermatitis

- Chronic radiation keratosis

- Chronic radiodermatitis

- Eosinophilic, polymorphic, and pruritic eruption associated with radiotherapy

- Fluoroscopy burn

- Radiation acne

- Radiation cancer

- Radiation dermatitis (radiodermatitis)

- Radiation recall reaction

- Radiation-induced erythema multiforme

- Radiation-induced hypertrophic scar

- Radiation-induced keloid

- Radiation-induced morphea

Although the exact etiopathogenetic mechanism of Ballantyne syndrome remains unknown, several authors have reported raised uric acid levels, anemia, and low hematocrit without hemolysis.

In most cases Ballantyne syndrome causes fetal or neonatal death and in contrast, maternal involvement is limited at the most to preeclampsia.

Respiratory complications are often cause of death in early infancy.

Marshall–Smith syndrome is not to be confused with:

- Marshall syndrome (aka.Periodic fever, aphthous stomatitis, pharyngitis and adenitis (PFAPA syndrome, see also: Periodic fever syndrome)

- Sotos (like) syndrome

- Weaver-Smith syndrome (WSS)

Roberts syndrome is an extremely rare condition that only affects about 150 reported individuals. Although there have been only about 150 reported cases, the affected group is quite diverse and spread worldwide. Parental consanguinity (parents are closely related) is common with this genetic disorder. The frequency of Roberts syndrome carriers is unknown.

Nevo Syndrome is considered to be a rare disorder. Since its first appearance in 1974, only a handful of cases have been reported. Studies have shown showing similarities between Nevo Syndrome with Ehlers-Danlos syndrome as well as Sotos syndrome. There is an astounding overlap of phenotypic manifestations between Nevo Syndrome and the more frequent Sotos syndrome, which are both caused by the NSD1 deletion. Sotos syndrome is an autosomal dominant condition associated with learning disabilities, a distinctive facial appearance, and overgrowth. Studies have shown an overwhelming occurrence (half of those involved in the study) of Nevo syndrome in those individuals of Middle-Eastern descent.

Nevo Syndrome is an autosomal recessive disorder. Most times in which a child is afflicted with Nevo Syndrome, both their parents are of average height and weight. It is only until after birth when the characteristic physical traits associated with disease are manifested, and the disorder is actually diagnosed. One study showed that despite the increased growth rates, the patient was completely healthy up until age 6, when he was admitted into the hospital. Nevo syndrome is usually associated with early childhood fatality. Children with Nevo Syndrome have a high occurrence of death due to cardiac arrest because their developing hearts cannot keep up with their overgrown body.

Schimmelpenning syndrome appears to be sporadic rather than inherited, in almost all cases. It is thought to result from genetic mosaicism, possibly an autosomal dominant mutation arising after conception and present only in a subpopulation of cells. The earlier in embryological development such a mutation occurs, the more extensive the nevi are likely to be and the greater the likelihood of other organ system involvement.

Overgrowth syndromes in children constitute a group of rare disorders that are typical of tissue hypertrophy. Individual overgrowth syndromes have been shown to overlap with regard to clinical and radiologic features. The details of the genetic bases of these syndromes are unfolding. Any of the three embryonic tissue layers may be involved.The syndromes may manifest in localized or generalized tissue overgrowth. Latitudinal and longitudinal growth may be affected. Nevertheless, the musculoskeletal features are central to the diagnosis of some syndromes such as Proteus syndrome. The time of presentation of children with overgrowth syndromes is an important contributor to the differential diagnosis. Children with some overgrowth syndromes such as Klippel-Trenaunay-Weber syndrome can be readily detectable at birth. In contrast other overgrowth syndromes such as Proteus syndrome usually present in the postnatal period characteristically between the 2nd and 3rd year of life. In general, children with overgrowth syndromes are at increased risk of embryonic tumor development.

Examples of overgrowth syndromes include; Beckwith-Wiedemann syndrome, Proteus syndrome, Sotos syndrome, neurofibromatosis, Simpson-Golabi-Behmel syndrome, Weaver syndrome, Sturge–Weber syndrome, Macrocephaly-capillary malformation, CLOVES syndrome, fragile X syndrome and Klippel-Trenaunay-Weber syndrome.

A syndrome is a set of medical signs and symptoms occurring together, constitutes a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". In some instances, a syndrome is so closely linked with a pathogenesis or cause that the words "syndrome", "disease", and "disorder" end up being used interchangeably for them. This is especially true of inherited syndromes. For example, Down syndrome, Wolf–Hirschhorn syndrome, and Andersen syndrome are disorders with known pathogeneses, so each is more than just a set of signs and symptoms, despite the "syndrome" nomenclature. In other instances, a syndrome is not specific to only one disease. For example, toxic shock syndrome can be caused by various toxins; premotor syndrome can be caused by various brain lesions; and premenstrual syndrome is not a disease but simply a set of symptoms.

If an underlying genetic cause is suspected but not known, a condition may be referred to as a genetic association (often just "association" in context). By definition, an association indicates that the collection of signs and symptoms occurs in combination more frequently than would be likely by chance alone.

Syndromes are often named after the physician or group of physicians that discovered them or initially described the full clinical picture. Such eponymous syndrome names are examples of medical eponyms. Recently, there has been a shift towards naming conditions descriptively (by symptoms or underlying cause) rather than eponymously, but the eponymous syndrome names often persist in common usage.

Sometimes, the skin will blister when it comes into contact with a cosmetic, detergent, solvent, or other chemical such as nickel sulfate, Balsam of Peru, or urushiol (poison ivy, poison oak, poison sumac). This is known as contact dermatitis. Blisters can also develop as a result of an allergic reaction to an insect bite or sting. Some chemical warfare agents, known as blister agents or vesicants, cause large, painful blisters wherever they contact skin; an example is mustard gas.

Pashayan syndrome also known as Pashayan–Prozansky Syndrome, and blepharo-naso-facial syndrome is a rare syndrome. Facial abnormalities characterise this syndrome as well as malformation of extremities. Specific characteristics would be a bulky, flattened nose, where the face has a mask like appearance and the ears are also malformed.

A subset of Pashayan syndrome has also been described, known as "cerebrofacioarticular syndrome", "Van Maldergem syndrome'" or "Van Maldergem–Wetzburger–Verloes syndrome". Similar symptoms are noted in these cases as in Pashayan syndrome.