Bleaching is essentially a process of lightening the color of your hair. Hydrogen peroxide is often used in combination with ammonia and a toner to both lighten and change the pigmentation or shade of your hair. And while bleaching can help provide you with a myriad of different hair colors, changing your overall appearance and even outlook, the actual process can negatively affect the health of your locks.
The process of bleaching can strip the moisture from your hair. As the bleaching solution comes into contact with the hair shaft, it causes the hair to enlarge, triggering a separation in the cuticle scales that make up your hair. Though this is necessary for the dye to penetrate the hair, thereby altering its color, it actually makes the hair much more porous than before. This can inevitably affect the moisture level of your hair, causing it to become dry and damaged.
There is also the potential for bleaching to cause hair breakage. Often referred to as a "chemical haircut," breakage is also a result of the porous nature of the hair after bleaching. Since the solution causes the cuticle scales to separate, prolonged exposure to the substance can continue to bring about further separation, causing the hair to become even more brittle. Previously bleached or dyed hair, as well as overly-processed hair is already porous, so application of bleach can instigate the same effect.
It isn't uncommon for the scalp to experience a certain sense of tingling as the bleaching solution comes into contact with the skin. However, it's possible for your skin to either have an adverse reaction or suffer a chemical burn from the product. In both situations, the tingling will change to a burning sensation. It may be accompanied by some redness, itching and the development of sores. Regardless of the reason for the reaction, the product should be immediately removed from your scalp.
Since your scalp is essentially made of the same basic proteins as you hair, it's likely to experience some skin discoloration along any area of the scalp that comes into contact with the bleaching solution. Time will help the skin return to its natural color.