Why do I need to do anything if my deck is made of Pressure Treated Wood?

Pressure Treated Wood is protected against rot and decay. Pressure Treated does not mean weatherproofed, in fact pressure-treating wood can make it more susceptible to moisture damage. Moisture damage leads to splitting, warping, and cracking, and can cause wood to become discolored and unattractive. Pressure treated wood also contains CCA, Chromated Copper Arsenate, and contains the dangerous chemical arsenic. As of December 30, 2003, CCA products cannot be used to treat lumber intended for residential settings. The US EPA (U.S. Environmental Protection Agency) does not recommend replacing your pressure treated wood structures; it does however suggest finishing them with oil-based semitransparent stains on a regular basis to reduce CCA exposure.