he rash is the skin lesion most common, characterized by congestive redness of the skin, diffuse or localized, disappearing when the vitropression (that is to say in support, notably through a watch glass) . It is usually the external manifestation of vasodilation, which when it is accompanied by exudation erythema gives a false character "papular".

Except in a few cases, the elementary lesion there's usually no other local changes.

The rashes are due to passive accumulation of venous blood. There may be cyanosis due to heart failure or respiratory failure, a acrocyanosis, frostbite, livedo reticularis or livedo racemosa.

The rashes are due to active vasodilation. They may be diffuse or localized.

* Among the diffuse erythema we recognize

The morbilliform erythema, resembling that of measles: those for measles, rubella, fifth disease, viral disease in the cocsackies, infectious mononucleosis, toxoplasmosis or iatrogenic, dys antibiotics, barbiturates, etc..

Erythema scarlitiniformes are those that evoke the stains caused by scarlet fever. These diffuse plaques bright red, slightly Granita to palpation, without an interval of healthy skin. They are hot or bitter, intensifying in the folds. They may progress to desquamation in large pieces.
They include scarlet fever, rubella, erythema caused by toxic shock syndrome staph, one of Kawasaki disease, or erythema iatrogenic, due to antibiotics, sulfonamides, or poisoning by mercury (erythema mercurial).

Roséoliformes erythema, characterized by small pink spots, pale and well separated from each other, are due to a virus or are iatrogenic (skin reaction to antibiotics, barbiturates ...). They include roseola, secondary syphilis, the sudden rash.

* Among the range is localized erythema

- Lucite,
- Intertrigo,
- The photodermatosis,
- Lupus erythematosus,
- Dermatomyositis and erysipelas

The rash may be localized due to emotional as erythema and appear modest countenance that.

Among erythrodermas, it ranks last psoriasis, contact dermatitis, atopic dermatitis, the drug eruptions and hématodermies and erythema migrans due to a bacteria of the genus Borrelia transmitted by tick bite (Lyme disease).

The telangiectasia is a permanent dilation of superficial vessels, forming linear streaks of bright red, sometimes anastomosing network and disappearing when the vitropression. It is hereditary or acquired.

* Hereditary disease Rendu-Osler, ataxia-telangiectasia, poikiloderma congenital angioma plan.
* Acquired: facial rosacea, scleroderma, stellate angioma in pregnancy or cirrhosis and hepatic veins.

Differential Diagnosis
* Purpura: will not clear the vitropression; changing color.
* Angioma Plan: congenital; vitropression the stump and revealed telangiectasia.
* Papules: infiltrated.

See also Bubble (damage)