ROAT or PATCH Test

[Guide]

When diagnosing any skin condition sometimes dermatologists perform a Repeated Open Application Test (ROAT) or a patch test. Ask your dermatologist about the following tests. 

ROAT
"The open application test is also sometimes called the “repeat open application test” or abbreviated as ROAT. It is a simple method of testing for allergic contact dermatitis (delayed-type allergy or type-4 hypersensitivity reaction). The product to be tested by open application is applied directly to a small area of skin. The application is repeated on several occasions and the treated area observed to see whether contact dermatitis arises." [1]

PATCH
"A patch test is a diagnostic method used to determine which specific substances cause allergic inflammation of a patient's skin. Patch testing helps identify which substances may be causing a delayed-type allergic reaction in a patient, and may identify allergens not identified by blood testing or skin prick testing. It is intended to produce a local allergic reaction on a small area of the patient's back, where the diluted chemicals were planted." [2]

Either test may be useful to help diagnose a skin condition in a patient with rosacea or sensitive skin or when differentiating erythema in skin conditions. 

Etcetera

Diagnosing Rosacea

End Notes 

[1] Open application test, DermNet NZ

[2] Patch Test, Wikipedia