Summary Background/purpose: The contact hypersensitivity (CHS) response has been used to assess ultraviolet radiation (UVR)-induced immunosuppression and to evaluate the photoimmune protection of different sunscreen preparations in vivo. Earlier reports of the effect of age and gender on CHS response have led to variations in inclusion criteria for participants in regards to age and gender in the study of sunscreen immune protection factor (IPF). Methods: This study is a retrospective analysis of data from 73 volunteers from prior CHS studies with the goal of determining the effect of age and gender in young and middle-aged adults on CHS response to dinitrochlorobenzene (DNCB) in unirradiated and UV-irradiated skin. Results: In patients aged 18–63 years, the effect of age on CHS response as well as on UV suppression of CHS response was not statistically significant. In the unirradiated (n=45) and UV-irradiated (n=28) groups, the CHS response between men and women was similar when the timing of DNCB application avoided the period within 5 days before or after the first day of the menstrual cycle. Conclusion: Within a certain range, 18–63 years, age does not significantly affect the normal CHS response and the suppression of CHS response by UV. This study also demonstrated that as long as certain days of the menstrual cycle are avoided when sensitizing women of reproductive age, gender does not significantly affect CHS response. Thus, within these parameters, CHS can be appropriately evaluated in healthy individuals without much concern regarding independent effects of age and gender.