Well, not BAD, but it loses its effectiveness over time. I didn’t know that. One day last week I went to treat a spot of mildew that keeps growing back in the caulk behind the kitchen sink faucet. I did this several months ago by soaking a strip of cloth in bleach and laying it on the mildewed area and leaving it there all day to soak into the caulk.
This time, it didn’t work at all. The mildew wasn’t fazed a bit! The bleach I had used was the last bit in a bottle that had probably been in my cupboard for over a year. Puzzled, I started searching the internet and immediately found this: http://chemistry.about.com/b/2014/01/31/chlorine-bleach-shelf-life.htm
Come to find out, the hypochorite that makes bleach bleach breaks down over time and breaks down faster when it’s in a hot place. A new bottle of bleach should stay powerful for 6 months at 70 degrees F. It’s still useful after that, but its strength gradually declines. So in my case I should buy the smallest bottle they offer because I rarely use bleach. Bleach stored in a hot garage will break down faster than bleach stored in an air conditioned room inside.
If there’s use-by date on my bottle of bleach I can’t find it. So I guess I’d be smart to mark each new bottle when I bring it home from the store with the date I bought it so I’ll know how much time I have left to use it up.