Hi Karen, here's one of the most recent Church statements on animal testing, where in paragraph 130 of his encyclical letter on ecology, Laudato Sii, Pope Francis wrote:
While human intervention on plants and animals is permissible when it pertains to the necessities of human life, the Catechism of the Catholic Church teaches that experimentation on animals is morally acceptable only "if it remains within reasonable limits [and] contributes to caring for or saving human lives".[106] The Catechism firmly states that human power has limits and that "it is contrary to human dignity to cause animals to suffer or die needlessly".[107] All such use and experimentation "requires a religious respect for the integrity of creation". [108]
Most of us haven't a clue as to whether products we're buying have been developed by means of animal testing, but because people have been questioning animal testing for beauty products, there have been a range of these goods which explicitly say that animal testing wasn't involved in producing them. So if you have a choice, it'd be better to use those products.
I don't think we can speak of sin whether or not you use these products, since as you say, a person's cooperation in the wrong of unnecessary animal experimentation is pretty remote, but the more people protest about this abuse and boycott those products, the quicker will producers find more ethical means of production.
Very best, Fr Brendan