Methods are provided for ascertaining and measuring RPTP-κ activity in response to insults such as UV irradiation and with respect to administration of a treatment and/or composition. Attenuation of EGFR activity by RPTP-κ affects aspects of photoaging, including damage to the skin, suppression of the immune system, DNA damage, and connective tissue degradation. Intervention with respect to the effects of photoaging can include protection of RPTP-κ from oxidation. The methods can be used for discovery of anti-aging treatments, adjuncts, or other preventative treatments, such as sunscreens.