Phenolic acids, a class of plant-derived polyphenols, have been studied for their antioxidant and skin-protective properties. Age spots, or solar lentigines, are primarily caused by oxidative stress and cumulative UV exposure, leading to hyperpigmentation. Scientific studies indicate that phenolic acids, such as ferulic acid and caffeic acid, can inhibit melanogenesis (the process of melanin formation) and reduce oxidative damage in skin cells. In vitro and some animal model research have shown that phenolic acids can modulate tyrosinase activity, a key enzyme involved in melanin production, and exert antioxidant effects that may protect skin from UV-induced damage.

However, while these mechanisms are promising and provide a plausible basis for their use, direct clinical evidence supporting the efficacy of phenolic acids in treating or lightening age spots in humans is limited. Most data are preclinical or from small-scale studies, and there is a lack of large, well-controlled clinical trials specifically examining phenolic acids for this purpose. As a result, while the use of phenolic acids is scientifically plausible and supported by some early research, the overall quality and quantity of evidence remain modest, justifying a rating of 2 on the evidence scale.