Are Preservatives Necessary in Solid Conditioners and Shampoo Bars? Test Results So Far

Welcome to Nov 16: day one of this little test on whether or not conditioner and shampoo bars require preservatives. 

If you didn't read the first part of this experiment, you'll find it right here.

Creating the Perfect Bacteria-Promoting Environment

To undertake this test, three conditioner bars from a suitable batch were selected. As I often test out different molds while I am testing out formulas, the 3 bars I chose have different sizes and shapes, but they are from the same batch.

One bar was unused and has remained so as the control bar. It is pictured at the top of the last post.

One bar was used regularly and allowed to air dry between uses, and the third was selected to enter 'conditioner bar waterworld'.

The bar that was chosen to live in water had already been in use for a couple of weeks and allowed to air dry between uses. It was nominated for the watery test purely because it fit into the dish. It's the little heart shaped number you see above.

The dish was filled with ordinary tap water and allowed to sit out on a shelf in my lab for observation.

The Test Begins

Every day, I checked the water - topped up when needed, took a picture, sniffed, and generally monitored for level of smooshy grossness. I was interested to see whether or not mould would grow and wondered how long it would take before it started smelling horrendous.

I'm not going to show you every picture because you would be bored to death scrolling through that many similar shots, so I picked out a few to show you progress.

And I better confess: there were a few days over the Christmas holidays where pictures were not taken and the bar managed to dry out. ( I was actually not working for a few days)

Day 5

No discernable difference in scent or feel (still solid when pressed slightly). No mould or other nastiness.

Day 13

No discernable difference in scent or feel (still solid when pressed slightly). No mould, but the color is now darkening.

Day 29

No discernable difference in scent or feel (still solid but slightly softer when pressed slightly). No mould, but the color continues to darken. It is more obvious that the bar is absorbing water.

Day 50 

Here is a comparative photo of the conditioner bars on day 50. I seriously did not expect this to go on for 50 days and what is even more surprising, it is still ongoing.

If you think the color overall looks like it has morphed somewhat from the creamy white you saw in the first post, you would be correct.

These bars contain an ingredient I suspected would turn the bar darker over time, and my suspicions were confirmed. (more on that in another post).

As for the question of adding preservatives or not...

It's a Judgement Call

If you feel more comfortable adding a preservative to a product designed to be preservative free or where preservatives are not even necessary, then who am I to stop you. Even though I (obviously) don't agree with you on that point, it won't make us enemies.

My own personal choice is to add only the ingredients necessary to a formula. I have heard many say they add preservatives 'just in case' or 'just to be safe', but to me this seems illogical.

If they aren't necessary, why add them?

This Test Continues

In this (still ongoing) test, it has been interesting to observe how well the bar has fared.

I was expecting mould and a vile stench to make its presence at one point, but nothing of the sort has happened - yet.

At this point, I think its fair to say if this solid conditioner bar can manage fifty days in a pool of tap water at room temperature, its a pretty clear indication it would easily survive normal use - even normal use for folks who are awfully slap-dash about the way they keep their products in the bathroom.

Do Tell

Have you ever put any of your products through the wringer?

This e-book shows you how to make a complete collection of preservative free skin and haircare products with only 21 ingredients.


SoapNerds said…
This is interesting but to send it out for a real test for mold & bacteria would make it much more scientific, IMHO. I know there is a cost involved but visual & scent observation don't tell the whole story and this may teach people that if something smells OK, it is OK. (and it is not always!)

Said with respect & thanks for all you put into this site.
LisaLise said…
Hi Soapnerds - Thanks for your comment. I totally understand your point. Just FIY: I have a colleague who has done the same with a similar product and their test has been ongoing a full year with no problems. :)
Anonymous said…
I purchased a solid conditioner that turned moldy after 1 month of being used... that really put me off from buying and making unpreserved products.
LisaLise said…
Hi Anon - thanks for sharing this. I can’t help wondering about what the formula might have been, but I absolutely understand how experiencing something like that could make you cautious.
Anonymous said…
As a microbiologist working in cosmetic preservative efficacy testing, I can tell you that your product can be crawling in bacteria and yeast and the product still look and smell exactly the same. Only looking for a mould is not a good indicator of product safety - especially when a product can also be supporting mould spores that you cannot see. In fact, there have only been two instances in the past few years (out of all the contaminated samples I see every week) where I have seen a product growing actual visible mould hyphae.
LisaLise said…
Hi Anonymous - thanks for sharing.