Table 1.

Classification of PINGs by their mechanism of action (MoA)

MoA category	Primary target	Principal PING(s)
1. Antioxidant/ROS scavenging	Neutralizing free radicals (singlet oxygen, superoxide) Activate NRF2 to upregulate intrinsic antioxidant enzymes	L-Ascorbic acid (Vitamin C) (●●●●○), α-Tocopherol (Vitamin E) (●●●●○), Tocopheryl acetate (●●●●○), Melatonin (●●●○○), N-acetyl-L-cysteine (●●●○○)
2. Compatible solutes	Stabilizing cellular structures by forming protective hydration shells around proteins, DNA, and lipids	Ectoine (●●●○○), mannitol (●●●○○), betaine (●○○○○)
3. DNA repair	Promoting excision and repair of photoproducts (e.g., CPDs)	Photolyase (●●●●○), T4 Endonuclease (●●●○○), SIK inhibitors (●●○○○)
4. Immunomodulation	DNA repair; inhibition of immunomodulatory cytokine release	Nicotinamide (●●●●○), Green tea extract (●●●○○)
5. Anti-inflammatory	Inhibition of NF-κB signaling; inhibition of UV-induced inflammatory cytokine release; inhibition of NOS	Epigallocatechin gallate (EGCG) (●●●○○)
6. Pigmentation modulation	Regulating melanogenesis	Isobutylamido thiazolyl resorcinol (●●●●○), 2-mercaptonicotinoyl glycine (●●●○○), p-coumaric acid (●●●○○)

Evidence strength is represented using a 5-point visual scale (●), based on the level and consistency of clinical evidence: ●●●●● = Very strong (multiple randomized clinical studies and consistent in vivo evidence). ●●●●○ = Strong (controlled human studies with supportive mechanistic data). ●●●○○ = Moderate (limited clinical evidence). ●●○○○ = Limited (primarily preclinical or inconsistent evidence). ●○○○○ = Preliminary (mechanistic or exploratory data only)

CPD cyclobutane pyrimidine dimer, NF-κB nuclear factor kappa-B, NOS nitric oxide synthase, SIK salt-inducible kinase