What type of chemical is mainly used for straightening hair?

Sodium relaxers are primarily used for straightening hair because they contain sodium hydroxide or similar compounds that work to break down the protein bonds in the hair. This process causes the hair to relax and become straighter. Sodium relaxers are specifically designed for this purpose and are highly effective on coarse or curly hair textures.

The reasoning behind the other options lies in the fact that while they may play a role in various aspects of hair care, they do not function as primary chemical straighteners. Amino acids are beneficial for strengthening and repairing hair rather than straightening it. Hydrogen peroxide is typically used in hair bleaching and lightening processes, affecting hair color rather than texture. Silicones are used to provide smoothness and shine but do not change the hair's natural curl pattern. Thus, sodium relaxers are distinct in their purpose for hair straightening.