Why Is Some Soap Not Vegan?
The most common reason for a given soap product to be unsuitable for vegans is that it contains fats or other products derived from animals (such as honey or other substances often used to add a certain fragrance).
It really isn’t hard for companies to make a vegan-friendly soap: you just need to use a plant-based fat (such as olive oil or coconut oil) instead of animal fats. And while the animal fats might be cheaper, soap producers are cottoning on to the fact that ethically minded consumers are willing to pay a premium to ensure no animals were harmed to allow them to clean their hands.
Tested on Animals
Aside from animal fats and other animal-derived ingredients, some other soaps are deemed problematic for vegans because they have been tested on animals, or are produced by companies that routinely tests on animals. Clearly such a company is not going to advertise this fact on their packaging, but those who don’t test on animals (and never have done) generally like to make this apparent, which makes things easier for vegan soap seekers.
Soap & Animal Testing
Since the ban on animal testing for cosmetics in the European Union in 2013 (that’s EC Regulation 1223/2009 on cosmetics, in case you were wondering!), most companies who produce soap have found alternative ways of testing their products. But that is not to say that some companies who produce soap do not test some of their non-cosmetic products on animals when they deem it appropriate. Also it is possible that soap imported from outside EU jurisdiction could have been tested on animals (though an increasing number of countries are implementing similar bans).
The best way to avoid soaps that have been tested on animals is simply to purchase from companies who explicitly state they are against animal testing (and always have been) and that their products have never been tested on animals.