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Practical Guide — Phototoxicity & the 3T3 NRU Test
A practical guide to phototoxicity assessment — why it matters, the UV-absorption pre-screen (OECD TG 101) and the in vitro 3T3 NRU phototoxicity test (OECD TG 432) — to secure light-exposed products.
What's inside
- Why phototoxicity matters for light-exposed products
- UV/visible absorption pre-screen (OECD TG 101)
- The in vitro 3T3 NRU phototoxicity test (OECD TG 432)
- Interpreting results and securing your regulatory dossier
When a product is exposed to light — especially UVA — it can trigger adverse effects on the skin or eyes. This light-induced toxicity is known as phototoxicity, and it is a key safety endpoint for cosmetics, topical drugs and any light-exposed formulation.
Before any biological phototoxicity test, the molecule’s ability to absorb light must be confirmed: according to OECD TG 101, a molar extinction coefficient threshold determines whether further testing is warranted. The in vitro 3T3 Neutral Red Uptake (NRU) phototoxicity test (OECD TG 432) then quantifies the phototoxic potential using a validated, non-animal cell model.
Who this is for
- Cosmetic formulators of light-exposed products
- Pharma teams developing topical / transdermal drugs
- Regulatory and safety assessors
Recommended citation
GenEvolutioN Scientific Team (2025). Practical Guide — Phototoxicity & the 3T3 NRU Test. GenEvolutioN Technologies.