Magnesium sulfate, aka Epsom salt, is a useful curl activator with some harmful results.

What is Magnesium sulfate?

Magnesium sulfate is an ingredient often touted as a natural curl booster or curl activator for hair. It is typically used in leave-in conditioners and curl enhancers, both commercially available and homemade, and it is applied via a spray-on delivery method.

Many people have noted that their hair often responds remarkably well to the initial application, but further uses yield dry tresses that behave in an unruly fashion.  Several explanations have been put forth for this phenomenon, but there still remains some confusion as to why it happens.

By delving into the protein structure of hair and curls, and how magnesium sulfate interacts with these, we can gain clear understanding of the mechanism by which magnesium sulfate enhances curl pattern and retention, and also why the effects seem short-lived and eventually become unpleasant.

Hair Keratin Protein

Other types of crosslinking also occur between the polypeptide chains, and they also contribute to the structure of the hair. These two additional types of crosslinking are achieved via hydrogen bonding and formation of salt bonds and are sometimes referred to as secondary bonds. However, both of these types are physical crosslinks, rather than chemical ones (imagine it as two strands taped together or two magnets attracted to one another versus two strands sewn together or melted and re-formed into one object), and are susceptible to disruption via mechanical forces (touching or brushing the hair, wind) or the presence of water (swimming, washing, humidity, rain).Proteins are polymeric molecules (also called polypeptides) made up of many repeat units of various amino acids. The sequence, type, and order of the amino acids vary greatly depending upon the function of the specific protein. Hair is comprised of keratin protein, a polypeptide particularly differentiated from other proteins for its large proportion of cysteine, a sulfur-containing amino acid.  These polypeptide strands are crosslinked (bound together into a three-dimensional network) via formation of covalent bonds between adjacent cysteine residues. This linkage is a chemical crosslink referred to as the disulfide bond, and is the source of the strength and physical configuration of the hair. As the degree of disulfide crosslinking in a strand increases, so does the amount of curl in the hair.

Perms enhance curls by breaking the disulfide bonds via chemical means, curling the hair tightly to physically restructure it, and then re-forming the disulfide bonds at a higher percentage. Several researchers have found that hair is stronger and curl retention is increased when magnesium sulfate is incorporated into the rinsing and neutralizing agent used to re-form the disulfide bonds. They also noted that its use enhanced the curl pattern and imparted a greater stability to high humidity.