Did you ever wonder why tires turn brown? Here is the reason: Modern rubber formulas used by tire manufactures contain an ingredient called Antiozonant. An antiozonant is a chemical that tire manufacturers add to the tire rubber to help prevent rubber degradation (cracking, splitting, oxidizing, and overall deterioration) due to the rubber’s interaction with ozone (an odorless gas that is part of the air we breathe). Quite interesting is the fact that tire rubber is designed to constantly work the antiozonant to the outside of the tire as it rolls – in this way, the outside surface of the tire is continually replenished with fresh antiozonant. This process provides the positive result of ozone protection, but the negative result of tire browning – once the antiozonant gets exposed to the ozone in the air, it turns brown due to oxidation. The technical term for this effect is blooming.