Silica gel is a highly absorbent material made from sodium silicate. Typically sold in granular form or in pre-sealed packets, silica gel is used to absorb moisture or vapour from consumer products such as food, medicine, leather goods and electronics.
Although classified by the FDA as a Generally Recognized as Safe (GRAS) product, all packets of clear silica gel carry a warning label or hazard symbol. Although technically non-toxic, silica gel's moisture-absorption properties can cause mild nausea, constipation and vomiting if ingested. Most poison control centres do not consider ingestion of clear silica gel to be an emergency.
A second type of silica gel is called "indicator" gel because of its ability to change colour when exposed to moisture. Indicator gel dyed blue using cobalt chloride, a toxic chemical believed to be carcinogenic and cause respiratory irritation, turns pink when exposed to moisture. If ingested, poison control or 911 should be called and informed of the ingestion of cobalt chloride.
Silica gel ingested through the eating of a packet or the eating of "clumping" cat litter will most likely cause a gastrointestinal upset that could include nausea and vomiting. Consumed in large doses or repeatedly over time, silica gel can cause intestinal blockage.
Silica gel, in dust form, can be used as a pesticide and desiccant to kill bugs associated with growing and storing crops. In dust form, it can cause irritation to the membranes of the nose and lungs if inhaled.
Patented by a John Hopkins University professor in 1919 and used to absorb vapours in gas masks during WWI, mentions of silica gel date back to the mid-1600s.
Despite its name, silica gel is actually sold as either a hard, granular bead or as dust.