There are a few words (i.e. ‘natural') in the beauty industry that are commonly thrown around by companies to make their cosmetic, toiletry or cleaning products sound safe. And why not? If it's true that is.
The problem is makers and creators of these products have varied ideas of what some descriptive phases actually mean, particularly those that are not standardised. ‘Dermatologically tested' is one such hazy phrase where you'll find a disparate collection of opinions. Unfortunately there are no standard industry wide definitions setting out how a product must be tested and manufacturers tend not to be forthcoming with this information.
Dermatologically tested could mean a product has been tested on human skin and proven not to cause irritation or allergies; that it has been tested on animal or human skin; and/or that it's been tested in a laboratory by a dermatologist. It really depends on who you ask.
So be careful, as some companies are even sketchy about whether or not their products even passed the tests. By saying ‘product X has been dermatologically tested' does not necessarily translate to ‘successfully dermatologically tested and safe for all human skin types'.
How do you know if a claim is true? If you can't find an explicit statement on the packaging, promotional material or website contact the company direct and ask them. If they don't give you a straight answer test it yourself by applying a small amount to the back of your hand and wait a few days to see the result. This is the best test of all since we all have different skin types and can react in different ways. The only way to really know if a product is safe for your skin is to try it out. Request a sample or test in store so that you're sure before buying.