Just about all elastomer rubbers are porous on the microscopic level. Silicone rubber falls in this range. All rubbers will absorb and release microscopic materials. We use silicone because when it releases the absorbed materials there are no toxins that can be absorbed by the body, like phthalates from urethane rubbers. But, because of this absorption and release mechanism inherent in all rubber products, the silicone must be washed with soap and water between uses. Do not dry silicone products with heat, just wipe dry or shake off excess water. The use of heat will drive off important substances in the silicone, shortening its useful life.
Silicone toys should be stored in a clean cardboard or wooden box that allows for humidity and vapors (odors) to leave the silicone. Do not keep in a plastic zip lock bag.
Be careful with the term "Silicone". Not all proclaimed "silicone" products are good silicone or pure silicone.
Pure silicone comes in two species, condensation cure and addition cure. Condensation cure uses tin as a curing agent and is very bad for human skin contact. Addition cure uses platinum to cure the product and passes strict cytotoxicity testing to be allowed to be implanted into the body, and very expensive.
Mass produced silicone toys are made on injection molding machines. Platinum cured silicone has to be modified to run correctly in these machines The cheapest way to modify silicone is to create blends of silicone and easily processed rubbers. This is why most "silicone" toys are not really pure silicone. The best way to ensure you are buying pure platinum cured silicone toys is to look for hand poured rubber products from small manufacturers.
Information from: Lead Designer for LuzArte Products with over 30 years of experience designing silicone products for the medical industry.