All amber is fossilized tree resin. Baltic amber in particular (mined from near the Baltic Sea) additionally contains a substance called succinic acid. When worn on the skin, body heat causes the amber to release an oil containing succinic acid, which when absorbed into the skin, works like a natural Ibuprofen, blocking pain and reducing inflammation.
Baltic amber has some of the highest concentrations of succinic acid found in nature. Commonly known as "teething jewelry" in Europe, Baltic amber jewelry has been a natural remedy for pain relief for hundreds of years.