The 3T3 Neutral Red Uptake (NRU) Phototoxicity Test, approved by the OECD, detects the viability of 3T3 cells after exposure to a chemical in the presence or absence of light.
Ingestion of pigments capable of producing singlet oxygen with activation by light can produce severe photosensitivity of skin (see phototoxicity, photosensitivity in humans, photodermatitis, phytophotodermatitis).