It's bad enough that you have to deal with the litter box at all. Clumping litter makes cleaning it a little easier, but the convenience may come with a price. The ingredient that makes it clump so well has been linked to cancer in cats, dogs and humans.
Silica is what makes it clump so well, but it's also what makes clumping litter dangerous. It is a known carcinogen and can lead to cancer. Skin contact with silica isn't the problem, but when cats inhale or ingest it, silica can be deadly. Besides cancer it can cause many other health problems, including difficulty breathing, digestive issues and bowel problems.
Fine silica dust particles are stirred up every time your kitty uses the litter box. As he walks around scratches and digs in the litter silica dust is stirred up into the air. He can't help but breathe in the particles, especially in a litter box with a top, and the silica then coats his lungs. Most cats use the litter box several times per day, so your cat is continuously exposed to the silica dust.
If breathing it in isn't bad enough, some of the silica dust also settles on his fur as he moves around the litter box. When he grooms himself, he ingests the dust. Many cats give their paws a good cleaning right after they leave the litter box, making the problem even worse.
Litters made from natural products are a good alternative to clumping litter. Those made from corn, cedar, recycled paper, wheat or other grains typically don't contain the silica that has been linked to cancer.