 Welcome to Chemical Hair Bonds, the hydrogen bond. A strand of hair has four chemical bonds, peptide, disulfide, salt, and hydrogen. Hydrogen is the fourth chemical bond in the hair and is a cross-link. Hydrogen and oxygen atoms form hydrogen bonds. Hydrogen bonds are the weakest of all the bonds. Hydrogen bonds are easily broken by water or heat. Hydrogen bonds create a physical change in the hair. That change is only temporary. The hair is wet, the hydrogen bonds are broken. As the hair dries, the hydrogen bonds form into their new shape. The hair has taken on its new, temporary shape. Hydrogen bonds are also changed with heat. When the hair is curled with an electric curling iron, the hydrogen bonds are reformed into a new, temporary shape. Hydrogen bonds are the weakest of all bonds in the hair. They are easily broken and reset with heat and water. Congratulations, you have completed Chemical Hair Bonds, the hydrogen bond.