The quick and dirty answer is chlorine from pools.
I spent the summer at alot of pools this year. One pool was great, but the other pools turned my hair into dry, sticky, itchy messes.
Chlorine is basically a disinfectant. The busier the pool, the more exposed it is, the more chemicals they put in it to keep it clean and pretty so we'll go swimming in it. But disinfectants are used to break down and remove dirt, oil, and bacteria. Our hair has dirt and naturally is oily to protect it from damage. See the problem?
In addition to the chlorine problems with hair, sometimes it's our hair itself that is predisposed to be damaged by chlorine. Color Treated Hair, Chemically Treated Hair, Dry Hair, Thin or Fine Hair, and Previously Damaged Hair are more susceptible to hair damage from chlorine.
According to Kendra Aahus, at About.com, there are a few suggestions to help protect your hair from chlorine damage.
1. "Saturate Your Hair with Water. Before you enter the pool, rinse your hair with clean tap water to saturate your hair. Have you ever noticed that a sponge will only absorb so much water, and once it's full the water just runs off? Your hair is similar to a sponge. If you saturate your hair with clean tap water, your hair will be less likely to absorb as much of the chlorinated water in the pool."
2. " Shampoo. Shampooing your hair immediately after chlorine exposure is the best way to remove the bulk of the chlorine and stop the damage it may be causing to your hair. A clarifying shampoo treatment is another way to keep chlorine build-up at bay."
I found last summer the only thing that made my hair not turn into straw was immediately washing it. For me, it wasn't just the straw factor, but my hair would itch so bad, I couldn't stand it.
I'll definitely be trying #1 next summer!