Porcelain veneers can’t make your breath or mouth smell. They are made from dental porcelain, and they cannot decay. If your breath has gone south, it’s likely that your oral hygiene is lacking. If plaque and food particles are left around the edges of your veneers (remember, they only cover the front side of the tooth), that will begin the process of decay, and that will make your breath smell bad. But it’s not the veneers at fault; it’s your lack of attentive oral hygiene. Step up your twice-daily brushing for two minutes and flossing once and you should reverse the bad breath if decay hasn’t yet taken hold.
Or, you may have had veneers placed elsewhere and the fit was not precise. When that happens, there can be gaps between the veneers and the surfaces of the natural teeth. That allows bacteria to work its way in there and it will begin to emit sulfur odors when the bacteria break down the sugars left in your mouth. This will also likely lead to decay.