Exhaust soot is a carbonaceous byproduct of combustion, consisting of microscopic carbon particles and unburnt fuel (hydrocarbons). In high-performance vehicles, especially those with aftermarket tuning or deleted catalytic converters, these hot particles are ejected and immediately bond to the rear fascia. Because soot is oily and abrasive, "dry wiping" it will cause deep micro-marring. Over time, the heat from the exhaust "bakes" these hydrocarbons into the clear coat, leading to a permanent yellow or brown stain. Safe removal requires a surfactant-heavy degreaser to lift the oils and encapsulate the carbon before it is wiped away.