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Understand the potential for phototoxicity following topical exposure of your individual ingredients, chemicals or pharmaceutical products.

Phototoxicity assessment is in our portfolio of in vitro toxicology services for the cosmetics/personal care, chemical or pharmaceutical industry. Cyprotex delivers consistent, high quality screening data under non-GLP conditions.

Phototoxicity and its measurement in vitro

  • Phototoxicity is defined as a ‘toxic response from a substance applied to the body which is either elicited or increased (apparent at lower dose levels) after subsequent exposure to light, or that is induced by skin irradiation after systemic administration of a substance’1.
  • The assay is appropriate for pharmaceuticals, chemicals or cosmetics/personal care products which absorb in the wavelength range of 290-700nm, and are applied to, or can reach, the skin or eyes.
  • Cyprotex’s phototoxicity service is a non-GLP screening assay performed using Balb/c 3T3 cells. The cells are incubated with increasing concentrations of the test article in the presence and absence of a non-toxic dose of UVA irradiation. Cytotoxicity is assessed via Neutral Red uptake.

The in vitro 3T3 NRU phototoxicity test is based on a comparison of the cytotoxicity of a chemical when tested in the presence and in the absence of exposure to a non-cytotoxic dose of simulated solar light.

1 OECD Guideline for the Testing of Chemicals 432: In Vitro 3T3 NRU Phototoxicity Test; April 2004


Phototoxicity assay protocol

Models Available Balb/c 3T3 mouse fibroblast cell line 
Number of Replicates/Concentrations 6 replicates at 8 concentrations of test article (3T3 cells)
Exposure Conditions Condition 1: 3T3 cells kept in dark chamber. 
Condition 2: 3T3 cells exposed to calibrated non-toxic dose of UVA.
Assay Controls Chlorpromazine (Positive control)
Endpoints Neutral Red uptake (3T3 cells)
Data Delivery Photo irritation factor (PIF)
Mean photo effect (MPE)
Phototoxic category


Data from Cyprotex's Phototoxicity assay

Figure 1
Graph illustrating neutral red uptake data for the positive control compound, chlorpromazine, in the presence and absence of UVA irradiation using 3T3 cells.
Phototoxic Potential CategorizationData from in vitro 3T3 Neutral Red Uptake test
No phototoxicity PIF < 2 or MPE < 0.1
Probable phototoxicity PIF between 2 and 5 or MPE between 0.1 and 0.15
Phototoxicity PIF > 5 or MPE > 0.15
Table 1
Interpretation of phototoxic potential using the in vitro 3T3 Neutral Red Uptake test.

PIF = photo-irritation factor
MPE = mean photo effect


1OECD Guideline for the Testing of Chemicals 432: In Vitro 3T3 NRU Phototoxicity Test; April 2004

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