Phototoxicity Testing Services – 3T3 NRU PT

Phototoxicity / Phototoxicology Testing

3T3 NRU PT phototoxicity
3T3 NRU PT phototoxicity

MB Research Labs is a leading in vitro toxicology laboratory that offers toxicological testing services to the cosmetic, chemical and pharmaceutical industries.

One of the more important assays offered in the 3T3 Neutral Red Uptake Phototoxicity (3T3 NRU PT) Assay. The 3T3NRUPT is used to screen test materials for the potential of causing photoirritation after exposure to the material and sunlight.

The 3T3 NRU PT was developed and validated in a joint EU/COLIPA project from 1992-1997. In 1996, the 3T3 NRU PT was recommended by OECD as an in vitro approach for the assessment of chemicals phototoxicity potential. In April 2004, the 3T3 NRU PT protocol was finalized and adopted as the OECD 432 protocol, In Vitro 3T3 NRU phototoxicity test.

The 3T3 NRU PT can be utilized to identify the phototoxic effect of a test substance induced by the combination of test substance and light and is based on the comparison of the cytotoxic effect of a test substance when tested after the exposure and in the absence of exposure to a non-cytotoxic dose of UVA/vis light. Cytotoxicity is expressed as a concentration-dependent reduction of the uptake of the vital dye – Neutral Red.

Substances that are phototoxic in vivo after systemic application and distribution to the skin, as well as compounds that could act as phototoxicants after topical application to the skin can be identified by the test. The reliability and relevance of the 3T3 NRU PT have been evaluated and has been shown to be predictive when compared with acute phototoxicity effects in vivo in animals and humans.

For more information about the 3T3 NRU PT and MB Research Labs….

Skin Toxicity Testing – In Vitro Toxicology

Mechanisms of Skin Toxicity

Topical application is the main route of skin toxicity, whether it is an intentional or unintentional exposure. Also, many consumer products and cosmetics are applied directly on the skin.

Skin Irritation

Skin irritation is the production of reversible damage to the skin following application of a test material for up to 4 hours. Signs of skin irritation are erythema or redness, edema or swelling as a result of the test material penetrating the stratified layers of the epidermis.

Skin Corrosion

Skin corrosion is the production of irreversible damage to the skin following application of a test material for up to 4 hours. Signs are necrosis throughout the epidermis and dermis layers of the skin.

Skin Sensitization

Skin sensitization is the induction of an allergic reaction in response to exposure to a test material.


Phototoxicity is a toxic response from a test material applied to the body which is ether elicited or increased after subsequent exposure to light, or that is induced by skin irradiation after systemic administration of a test material.

MB Research Labs has an extensive capabilities list with in vitro assays targeting this areas of skin toxicity. We are able to utilize 3D tissue cultures and cell culture techniques to assess the safety of your test material for skin toxicity.

In Vitro Toxicology Testing