What is Glycerin? 

In scientific terms, glycerin is a simple organic molecule with three hydroxyl groups attached to the carbon chain. Its chemical structure is shown below. 

It has a slightly sweet taste and is a viscous liquid that easily dissolves in water. Glycerin is manufactured at a large industrial scale, mainly as a by-product of saponification (soap making, where vegetable fat or animal fat is hydrolyzed using sodium hydroxide).1 

The glycerin molecule is highly hygroscopic. That means it attracts water molecules from the air. This inherent property defines the characteristic features of glycerin and its applications. 

Glycerin is known by other names, such as:

• Glycerine (British English) 
• Glycerol 
• Propane-1,2,3-triol 
• 1,2,3-Propanetriol 
• Propanetriol 
• 1,2,3-Trihydroxypropane 

Safety of Glycerin in Skin and Hair Care Products 

Glycerin has been around for centuries. There are no known adverse effects or safety hazards for skin and hair care consumers, which is great.

Curly hair folk are primarily concerned about how well it does or doesn’t work for hair care. The safety of glycerin has never been a considerable concern. 

It can be added in concentration levels ranging from 2.0% to high up to 50% of the formulation (maybe even higher), depending upon the task and nature of the product.

Glycerin is a green and vegetable-derived naturally occurring ingredient with no adverse impact. 

Glycerin’s safety and toxicology have recently been reviewed in the International Journal of Toxicology, and experts found it safe in present-day cosmetics. Therefore, it is perfectly safe to use.² 

How Does Glycerin Work for Hair? 

Glycerin is a humectant having good water-binding ability and holding capacity. This feature is due to three hydroxy groups attached to the carbon chain. 

Glycerin binds water molecules via hydrogen bonding. The magnitude of water molecules binding glycerin molecules depends upon osmotic pressure and humidity level (availability of water molecules in the air). This characteristic property is exploited in hair care formulations. 

Glycerin-containing products (shampoo, conditioner, mask, or gel) attract water molecules, raising the hair’s moisture level. This moisture boost in hair fiber varies and depends on multiple factors. 

The water-holding capacity of hair varies with hair condition, protein level, porosity, damage, and external humidity level.

Porous hair fibers have a large pore size at the cuticle layer, and thus more moisture levels can penetrate the hair structure.  

Glycerin for Hair: Is it Good or Bad? 

Water is the key to hair life. Glycerin could be good for your hair, yet it may also have a negative impact. 

Its efficacy depends upon hair conditions and external weather conditions. Glycerin significantly improves hair moisture and helps address skin and hair dryness.

Hair dryness can indict significant damage like brittleness and loss of luster and becomes difficult to style and manage. 

Hair water uptake occurs via a dynamic balance system where adsorption or desorption varies with different humidity conditions. It is a “Two Way Traffic.”

Hair absorbs or may desorb water depending on the surrounding humidity. Moderate water absorption by hair improves health, quality, and outlook. 

However, an excess of anything is bad. High levels of glycerin may cause excessive water uptake, making hair swell and increasing its diameter.

More moisture in hair fibers breaks the hydrogen bond of keratin protein, thus, under high humidity conditions, making hair weak. 

Damaged hair fibers are more prone to this problem and are known to suffer severely. This is due to higher porosity and more space for water molecules to fill.

People with pre-damaged hair should take extra care to reduce the use of glycerin products. 

The Cons of Using Glycerin on Hair 

Adverse effects or cons are usually present with any great product or ingredient. That also goes for glycerin. Here are some ways glycerin can negatively impact your hair: 

• Excess or overuse use can lead to damaged hair. 
• It can cause greasiness and build-up. 
• Hair and scalp can become dry and flaky. 
• It can make hair look weighed down. 
• Overuse can lead to frizziness from excess moisture. 

How Glycerin Affects Hair During Summer and Winter 

Your hair responds to glycerin and behaves differently during summer and winter. The two seasons have different temperatures and humidity levels, and both factors influence the hygroscopic activity of glycerin. 

Summer: 

During summer, glycerin is an excellent choice for hair hydration therapy. The humidity is generally around 50-65 %RH level, thus having a balanced moisture level in the air.

A mixture of glycerin and natural oils or butter boosts the hair’s moisture content, lubricity, and tactile properties. 

Winter:  

In winter, the air is dry, with low temperatures and humidity. Frosty windy conditions may also be present. Glycerin may not be a good option for your curls under these conditions.

It would attract water molecules inside the hair and scalp cells instead of drawing them from the air. 

That means more water molecules outflow from the hair surface, making hair and scalp even drier. Glycerin should be avoided in cold winter conditions (especially for curly and damaged hair).

Emollients and oils are better for preserving the internal moisture level, lubricating the surface, and minimizing water loss.