Deep Conditioning: Effect of Time and Temperature/Heat

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For the past couple of weeks we have been talking deep conditioning. Today is the turn of two factors that are really key namely temperature (should you use heat when conditioning?)  and time (should you leave a conditioner on for hours?).

 Now for the purpose of this post, I will again define a conditioner as a water based conditioner (deep, intensive, mask or rinse out). If you are using oil, this is completely different and its own rules apply.

So will heat and time affect conditioning? The quick answer

Increased time and temperature do increase the amount of conditioner adsorbed to the surface of hair. The maximum time is 20-30 minutes and the maximum temperature is around 35°C.  

The long answer

I am being very general in this post because the fact is that every single ingredient that can adsorb and/or penetrate into hair (e.g surfactant or protein) actually has its own unique behaviour when added to a conditioner. This is also affected by other ingredients in the conditioner.  However there are common similarities in behaviour and these are the ones I wish to emphasise.

1.  Increasing the time you leave conditioner on hair allows more of it to adsorb with a maximum adsorption at 20- 30 minutes.

The key ingredients that can stick to hair (surfactants, hydrolysed protein, silicones, polyquats etc) will do so within seconds of applying the conditioner. If left on hair for longer, the amount will in general double within 10 minutes. If left on for another 10-20 minutes, the amount will increase by another 60-100% of the mark set at 10 minutes.

However after 30 minutes from initial application, there are no more increases in conditioner adsorbing to hair. The reason for this is that the hair conditioner simply has no more places on the hair where it can stick to.......all gaps which it can plug and all surfaces where it can attach are occupied.

The general graph that is obtained looks something like this

The relationship between conditioning time and adsorption

If you look at the 10 minute mark, you can see about 5% is on hair and at the 30 minute mark this increases to 10%. However at 40, 50 or 60 minutes there is no further increase, it just stays at 10%. Please do note that the numbers  5% and 10% are NOT real measurements. Adsorption is usually much lower than this (even as low as 0.01%) but for ease of digesting the information I picked simpler numbers like 5 and 10.

2. Increasing the temperature of a conditioner to surface body temperature (around 35°C) increases adsorption of a conditioner

Temperature increases the adsorption of conditioner such that slightly more can stick to the surface.  Generally tests are not performed much higher than 35-40°C in order to not burn the skin.  The graph looks something like this

 

There are two main lines in the graph one in blue at 20°C and another in orange at 35°C. What you see is that the orange line is shifted just slightly about the blue one. This means when conditioner is heated to 35°C, at 10 minutes there is slightly more than 5% on hair and at 30 minutes there is slightly more than 10%. Therefore temperature increases adsorption. The rule however remains the same in terms of no further conditioner sticking to the surface after 30  minutes.

Other influencing factors

1.  pH : The pH of your conditioner matters. In general pH between 6-7 work well to increase adsorption to hair. Below and above this range, the behaviour of the conditioner can become a little more erratic
2. Ingredient Quantities: Conditioners are different and contain different quantities of ingredients. For example, a conditioner which contains 0.2% hydrolysed protein will be able to leave about 20% more protein on the surface of hair compared to one which has 0.1%.  The result is more dramatic for surfactants with a 0.2% conditioner able to adsorb 80% more to the surface than a conditioner with 0.1% surfactant. The thing is, manufacturers will not tell you how much is on the jar, so you have to try the product and trust that your hair will tell you whether the product has too much or too little of the ingredient you are looking for.

References

J Soc Cosmet Chem, pp 259-273, 1992
J Soc Cosmet Chem, pp 351-359, 1991
J Soc Cosmet Chem, pp135-152, 1969
 
I will put up a summary post next week in combination with your key questions from the series. This is probably one of the more complex posts that I have put up so if you do not understand anything here, feel free to shout!