Why are some cosmetic ingredients added hot and others added cold

Formulating cosmetics can be a lot like cooking.  And just like when you are making lunch or dinner, some dishes and cosmetic formulas must be heated and others can be mixed at room temperature.  Here are some reasons there is a difference. 

Room Temperature Formulating

Ideally, you would be able to formulate all your products at room temperature (RT). There are a number of benefits such as

  • Faster to make
  • Requires less energy input
  • Easier to make adjustments
  • Less chance of ingredient breakdown

Of course, there are some downsides like increasing the chance of contamination or getting inadequate blending, but lower temperature formulating is usually the ideal.

Unfortunately, there are a number of ingredients that you can’t add at lower temperatures plus there are formulations that just won’t form at a lower temperature.

Why heat cosmetic formulas

Cosmetic formulations are heated for a few reasons:

1. Speeds up formulation: While formulating at RT can be quicker, this is not always the case. Some ingredients will more quickly dissolve in your solvent if they are heated up. For example, mixing salt crystals in cold water takes a lot longer for them to dissolve than in hot water.

2. Some ingredients need it: There are a number of ingredients used in cosmetic formulating that have a melting point that is higher than room temperature. In general, you want to mix things together that are in a liquid state. If you’re using an ingredient like Cetyl Alcohol or Glyceryl Stearate, you’ll have to heat your formula to above the melting point of these materials if you want to incorporate them into the formula. It doesn’t matter how long you mix Cetyl alcohol in water, at RT it won’t dissolve.

3. Make some formulas possible:  While it’s possible to mix the oil phase and water phase at RT, it’s not likely that you’ll be able to produce a stable emulsion using standard emulsifiers. In fact, some mixes of oil and water will not form any emulsion at a lower temperature. Heating your different phases, then blending them at a higher temperature helps make smaller particles that will then be more stable.

4.  Makes it easier to fill: Typically, lower temperature batches tend to be thicker. This can be a challenge when you are trying to fill the formula into a bottle or finished product container. For this reason formulas are heated up to around 35C. This keeps the formula fluid and makes it much easier for filling. As it cools down in the package it will thicken up.

Ingredients added as you cool down formula

While there are a number of benefits to hot batching, there are some ingredients that you shouldn’t add hot to your batches.  This is because they can chemically change when heated. Ingredients like formaldehyde donor preservatives will convert to formaldehyde too quickly so they lose effectiveness. Some of the components of the fragrance will evaporate off so the product won’t smell right. Some proteins or enzymes will chemically denature if heated too high. Many botanicals will chemically degrade if heated too high.

So, ingredients like fragrances, heat-sensitive cosmetic preservatives, and active ingredients are all added at cooler temperatures.

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