On the WD40 website they have a FAQ section. Here's some of it:
What does WD-40 contain?
While the ingredients in WD-40 are secret, we can tell you what WD-40 does NOT contain. WD-40 does not contain silicone, kerosene, water, wax, graphite, chlorofluorocarbons (CFCs), or any known cancer-causing agents.
What does WD-40 do?
WD-40 fulfills five basic functions:
1. CLEANS: WD-40 gets under dirt, grime and grease to clean. It also dissolves adhesives, allowing easy removal of labels, tape and excess bonding material.
2. DISPLACES MOISTURE: Because WD-40 displaces moisture, it quickly dries out electrical systems to eliminate moisture-induced short circuits.
3. PENETRATES: WD-40 loosens rust-to-metal bonds and frees stuck, frozen or rusted metal parts.
4. LUBRICATES: WD-40's lubricating ingredients are widely dispersed and tenaciously held to all moving parts.
5. PROTECTS: WD-40 protects metal surfaces with corrosion-resistant ingredients to shield against moisture and other corrosive elements.
What about using WD-40 on my sports equipment?
WD-40 is safe and effective to use on all types of sporting goods. Use WD-40 on your bike to clean, degrease and lubricate your chain, derailleur, gears, cogs, and moving parts. It will help remove stickers. Use WD-40 to clean and protect your gun. It will prevent corrosion and it won't damage bluing. Spray it on dirt bikes to protect parts and prevent mud from sticking. Use it on watercraft to protect metal surfaces from corrosion and to drive out moisture. WD-40 is also great for cleaning golf clubs and preventing rust on hockey skate blades.