Pathogenesis
Potential explanations include

Atypical immune recognition of autologous skin antigens
Stimulation of normal T cells by changing skin constituents
Lower threshold for skin irritation
Spreading of infectious antigens causing a secondary response
Hematogenous dissemination of cytokines from the primary site of inflammation

Diagnosis
Although there are a multitude of varying appearances, the id reaction often presents with symmetrical red patches of eczema with papules and vesicles, particularly on the outer sides of the arms, face and trunk which occur suddenly and are intensely itchy occur a few days to a week after the initial allergic or irritant dermatitis. Most commonly, athletes foot can lead to localised vesicles on hands, bacterial infections to erythema nodosum and herpes simplex virus to erythema multiforme.The diagnosis is frequently made by treating the initial triggering skin problem and observing the improvement in the eczematous rash. Both the initial skin problem and the id reaction must be observed to make the diagnosis.Not all dyshidrotic rashes are 
id reactions, but id reactions are often dyshidrotic-like.Initial tests may include isolating a fungus by taking a swab and sending it for culture. Patch testing may be considered if there is suspicion of allergic contact dermatitis.A skin biopsy is rarely necessary, but if done mostly shows an interstitial granulomatous dermatitis, some lesions being spongiotic. Id reactions cannot be distinguished from other skin diseases by histopathology. However, they can be distinguished from other id reactions by histopathology. Differential diagnosis
Other rashes that occur in a widespread distribution can look like an id reaction. These include atopic dermatitis, contact dermatitis, dyshidrosis, photodermatitis, scabies and drug eruptions.
Treatment
Id reactions are frequently unresponsive to corticosteroid therapy, but clear when the focus of infection or infestation is treated. : 81  Therefore, the best treatment is to treat the provoking trigger. Sometimes medications are used to relieve symptoms. These include topical corticosteroids, and antihistamines. If opportunistic bacterial infection occurs, antibiotics may be required. Prognosis
A full recovery is expected with treatment. Recurrent id reactions are frequently due to inadequate treatment of the primary infection or dermatitis and often the cause of recurrence is unknown. Epidemiology
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. History
The suffix -id has its origins in Greek, referring to a father–son relationship. Josef Jadassohn (1863–1936), the German dermatologist that coined the term id, had observed a dermatophytosis causing a secondary allergic skin dermatitis. In 1928, Bloch recorded that the peak of the dermatophyte infection corresponded with the id reaction. See also
Candidid
Dermatophytid
Leukemid
List of cutaneous conditions

References


== External links ==