This study analyses the ability of four non-invasive techniques (laser Doppler velocimetry, evaporimetry, chromametry and corneometry) to discriminate between irritant and non-irritant products, when compared to appropriate controls, and to detect subliminal changes in barrier function and erythema. These changes, which remain undetectable in the traditional visual and palpable clinical assessment, can be used as early reactions that are followed by the development of overt skin irritation. Laser Doppler velocimetry and evaporimetry were good discriminators between irritant and non-irritant substances, whereas corneometry and chromametry did not clearly distinguish between them. Laser Doppler velocimetry and evaporimetry detected early stages in the development of an irritant reaction before it became visible, but chromametry was not able to detect an early irritant response. It was concluded that non-invasive measurements could improve the quality and relevance of data obtained from human irritation testing, since the data they provide are objective, quantitative and sometimes subclinical, which also allows the concentration of a positive control to be reduced, resulting in the induction of less skin damage in human volunteers and reducing the ethical concerns related to the deliberate induction of an irritant response in a 'healthy' volunteer.