Ceramic tile usually has a glaze on the surface that gives it color and protects it from moisture. Stone tiles have sealants that also protect them from stains. While these layers are important, when they are applied in heavy coats they can dry to a slippery finish, which poses a risk for falls and accidents. In most cases, the slippery feeling will go away in time as the glaze or sealant dries and starts to wear. A thorough cleaning can often increase friction as well.
Clean your tile floor often to keep the floor rough enough to avoid slips and falls. As dirt and grime build up on tile, they form a new layer on the surface, which can create smooth, slippery tiles. Sometimes cleaning with the wrong products can also increase slipperiness. Use a product that is designed to clean ceramic or stone tile.
When you first apply grout to your floor, some of the grout is scraped off to the sides where it stays on the tile. When you clean your floors afterward, any lingering grout can form a haze on the tile, which can lead to slipperiness. Fully clean your tile with a strong detergent to remove this haze after grouting.
Sometimes your tile floors can become slippery because of the conditions around the tile. For example, bathroom tile that becomes wet may also be slippery. In these cases, it is better to use rubber mats and other surface coverings rather than damage your tile floor trying to increase its friction.