Psoriasis is a chronic inflammatory cutaneous disease, affecting 3% of the French population. Among psoriatic patients, 80% feel pain or cutaneous discomfort related to their pathology.

Neurogenic inflammation's role in psoriasis has recently been put forward by a study showing that TRPV1 ion channels are necessary to establish psoriasiform inflammation in mice.

The investigators hypothesize that there is a link between cutaneous sensory neuropathies and altered cutaneous microcirculation during psoriasis.

In order to test this hypothesis, local vasodilators will be delivered to patients by iontophoresis and their skin blood flow in response to these molecules will be followed by laser Doppler recordings. Two recordings will be performed for each patient, both on a psoriasis plaque and on uninvolved skin, in order for the patient to be his own internal control.

Inclusion Criteria:

• Type I psoriasis
• Psoriasis plaques on the patient's back

Exclusion Criteria:

• BMI > 25
• Diabetic patient
• Arteriovenous disease history
• Ongoing anti-inflammatory treatment
• Major cardiovascular history (<3 months)
• Hypertension
• Topical treatment on the back skin (<7 days)
• Systemic treatment (steroids, methotrexate, retinoids, cyclosporine) or phototherapy (<1 month)
• Pregnant women
• Subject within exclusion period following a previous or ongoing biomedical study