The concept of UV radiation hormesis: evidence, mechanisms and implications

Ultraviolet (UV) radiation (comprising UVA, UVB, and UVC wavelengths) lies in the non-ionizing region of the electromagnetic spectrum and is a key environmental factor affecting living organisms. While excessive UV exposure is well known for its harmful effects - such as DNA damage, oxidative stress, and cellular dysfunction - mounting evidence indicates that low-dose UV can induce beneficial adaptive responses (hormesis) in biological systems. This review offers a comprehensive synthesis of UV-induced hormetic effects across diverse organisms, with particular emphasis on plants and animals. We highlight examples of beneficial outcomes under mild UV exposure, including enhanced growth, strengthened pathogen resistance, and elevated secondary metabolite production in plants, as well as improved stress tolerance and reproductive performance in animals. These benefits are underpinned by molecular mechanisms such as upregulation of antioxidant defences, activation of DNA repair pathways, and accumulation of protective biomolecules. The review also explores practical applications of UV hormesis in agriculture - for instance, using controlled UV treatments to boost crop resilience - while cautioning against the risks of excessive exposure. By illuminating the balance between the beneficial and detrimental effects of UV radiation, this synthesis provides a broad perspective to guide the safe application of low-level UV in biological systems and identifies promising directions for future research.