Posted By Chris Packham Tony If you consult regulation 2 of COSHH, defining what constitutes a dangerous substance and look at item (e) you will see that any substance, even water, has the potential to be something that would fit this description. It is all about how the substance is used. Strictly speaking, therefore, the answer to your question has to be to consider the level of exposure and the potential that this has to cause damage to health. As a general rule water-mixed metalworking fluids are more damaging to the skin than the neat oils. However, in order to achieve adequate performance all such products will contain substances that, in contact with the skin, can cause damage. Skin damage is, of course, only one potential result of exposure, but the evidence is that it is more common that respiratory effects due to inhalation. Chris