Skin prick test (SPT) was used for diagnostic test for type 1 hypersensitivity. The efficacy and safety of SPT were proved. The positive control of SPT is histamine.

In Thailand, the most common concentration of histamine for SPT is 10 mg/ml. However, in some practice they use other concentration (1, 2.5 mg/ml).

This study will find the proper concentration of histamine for positive control use in SPT.

Appropriate concentration of histamine positive control is important in interpretation the result of skin prick test.

Inclusion Criteria:

• Parcitipate person who attented allergy clinic, ENT clinic
• Legible in Thai language

Exclusion Criteria:

• Patient cannot withhold antihistamine drug
• Pragnancy and lactation mother
• comorbid disease such as cardiac disease, liver, renal, hypertension and severe asthma