Kolin Powick has added another excellent article to the Black Diamond QC Lab blog about acid damage to climbing gear. He received an email from a climber whose harness had inexplicably failed while being lowered on a top rope. It turned out the harness had been exposed to an acid - an interesting tell-tale sign is discolouration in the stitching of the waist loop. Otherwise the harness looked in generally reasonable condition, but the stitching had turned pink/red as opposed to the normal grey colour.
The left hand harness has been exposed to a household product containing hydrochloric acid, and sulphuric acid on the right. Image from Black Diamond
Kolin tests the effect of about a dozen different household goods on the strength of a harness. Some are catastrophic, some have little effect - but it's not always obvious which will cause damage and which won't.