Extracellular low pH affects circadian rhythm expression in human primary fibroblasts

► Viability of human skin primary fibroblasts at pH 6.7 and 7.2 are comparable. ► Robust and sustained circadian rhythms are observed at pH 6.7 and 7.2. ► At pH 6.7 period length is about two hours shortened and amplitude is increased. ► The effects of exposure to pH 6.7 on the period are reversible.