In vitro phototoxicity test 3T3 NRO – OECD 432

Phototoxicity refers to a toxic reaction triggered by the exposure of a chemical substance to light, generally in the UV-A range. This phenomenon is particularly monitored for cosmetic, pharmaceutical, and dermatological products intended for cutaneous or ophthalmic use. The 3T3 NRU , validated by the OECD (OECD guideline 432 ), is a in vitro for assessing this risk without resorting to animal testing.

Test objective

This test aims to determine whether a substance or formulation has phototoxic potential in the presence of UV light. It allows us to:

• Demonstrate the safety of a photosensitive cosmetic ingredient or excipient
• Complete a cosmetic or REACH regulatory dossier
• Select safe ingredients for products exposed to light (sunscreen, day creams, perfumes, etc.)
• Identify cellular effects induced by combined exposure to a substance and UV radiation

Principle of the 3T3 NRU method

The test is based on the exposure of murine Balb/c 3T3 fibroblast cells to the tested substance, with or without exposure to UV-A radiation. Cell viability is then measured by Neutral Red Uptake, a dye that accumulates in the lysosomes of living cells.

A significant decrease in cell viability after UV exposure compared to the unirradiated sample is interpreted as a phototoxic response.

Methodology

• Preparation of a range of concentrations of the tested product
• Application on 3T3 cells under dual conditions: with and without UV
• Controlled dose UV-A irradiation
• Incubation, then addition of neutral red dye
• Spectrophotometric reading of absorbance
• Calculation of the Phototoxicity Index (PIF) and/or the Photo-Irritation Factor (MPE)

Matrices involved

• Cosmetic products (sunscreen, creams, gels, lotions)
• Excipients, perfumes, UV filters
• Chemical substances or plant extracts used in formulation
• Topical medications or dermatological products

Why choose YesWeLab?

YesWeLab connects you with laboratories specializing in regulatory studies and phototoxicity, equipped with calibrated equipment for the OECD 432 test. All tests are carried out according to good laboratory practices (GLP), with full traceability of results and tailored support.

Our team helps you define relevant concentrations, interpret results and integrate them into your safety dossiers (CPSR) or REACH/BPR registration dossiers.

See also:

• In vitro eye irritation test – OECD 492
• Skin corrosion – OECD 431
• Micronucleus test – OECD 487