Thein vitrosafety and antioxidant potential ofCalendula officinalisflower head extracts was investigated. The effect of different concentrations (0.125, 0.5, 1.0, 2.0 and 5.0% (v/v)) ofCalendulaextracts on human skin cells HaCaTin vitrowas explored. Doses of 1.0% (v/v) (0.88 mg dry weight/mL) or less showed no toxicity. Cells were also exposed to theCalendulaextracts for either 4, 24 or 48 h before being exposed to an oxidative insult (hydrogen peroxide H2O2) for 1 h. Using the MTT cytotoxicity assay, it was observed that two independent extracts ofC. officinalisgave time-dependent and concentration-dependent H2O2 protection against induced oxidative stressin vitrousing human skin cells. Pre-incubation with theCalendulaextracts for 24 and 48 h increased survival relative to the population without extract by 20% and 40% respectively following oxidative challenge. The antioxidant potential of theCalendulaextracts was confirmed using a complimentary chemical technique, the DPPH• assay.Calendulaextracts exhibited free radical scavenging abilities. This study demonstrates thatCalendulaflower extracts contain bioactive and free radical scavenging compounds that significantly protect against oxidative stress in a human skin cell culture model. Copyright © 2014 John Wiley & Sons, Ltd.