- Possess Fitzpatrick skin types I (always burns easily; never tans), II (always burns easily; tans minimally), III (burns moderately; tans gradually), or IV (rarely burns; tans with ease) that will not interfere with the evaluation of any skin responses (Fitzpatrick 1988). Determination of skin types will be based on sunburn and tanning histories, as well as subjects' opinions of their responses to the first 30 to 45 minutes of sun exposure.