The Scrub Evaluation

The first ever scrub evaluation we did started unintentionally, with no plans or design.

It was more of a “Hey, how about we’ll each bring a scrub that we made, and then let’s exchange notes!!”

That ‘how about’ moment (via text message) led to 30 minutes of non-stop scrubbing, notes taking and discussion. At the end of our first scrubbing evaluation (or eval for short), we were left with ultra-smooth hands that slightly hurt because of the extensive scrubbing. On the bright side, we went out declaring we now have ZERO dead skin. And it glows. Probably even in the dark.

Because there weren’t any rules or guidelines, we made five very different types of scrubs.

This is what we made:

  • Puja – Grapefruit Turbinado Sugar Scrub (P1)
  • Janette – Rose and Lavender Sugar Scrub (J1), Coffee Coconut Sugar Scrub (J2)
  • Brooke – Oatmeal Brown Sugar Scrub (B1), Lemon Scrub (B2)

This is the breakdown of what went into each scrub.

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To determine effectiveness and desirability, we created a simple scoring system centering on moisturizing factor, scent desirability and scrubbing effectiveness.

Each is ranked on a number scale – 1 being least desirable and 10 being most awesome.

We then gave our honest, brutal feedback and it quickly became apparent that the three of us have very different perspectives on how a good scrub should behave.

There are, however, common points as observed from boxplots plotted for each factor.

1.      Scrub Effectiveness – Data and Observations

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  • We found that white sugar generally scrubs better than brown sugar. Brown sugar is way too fine and dissolves quickly under just a tiny bit of water. Blend of both might negate this issue, while maintaining gentleness.
  • We all agreed that turbinado sugar is too rough on the skin. It actually hurts a lot more for me because I generally scrubbed really hard. There were scratches resulting from the scrub on my knuckles, and I dare not imagine using it on my body. It would, however, be perfect in a foot scrub.
  • We thought oatmeal was gentle. In fact slightly too gentle even with addition of brown sugar. It was wildly lacking in oomph factor in the scrubbing department. The only saving grace was that Brooke didn’t own any food processor. Lack of food processor, and the refusal to spend hours chopping oatmeal into fine dust resulted in large granules of oatmeal that still delivered some scrubbing power. But because her oatmeal was so chunky, adding coconut oil resulted in a scrub that smells and looks like a yummy granola bar. Not willing to give up on that yummy smelling scrub, we agreed that we need to look into a optimal oatmeal granule size.

2.       Moisturizing Factor – Data and Observations

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  • We had 4 different oils that day – almond, safflower, coconut and olive oil. Olive oil and coconut oil, while really moisturizing, leaves a pretty obvious greasy residue on our skin, a feeling which both Puja and me were not very keen on.
  • On the other end of moisturizing spectrum, we found that almond oil and safflower oil are really quick absorbing; hence it is the least greasy of the five scrubs. But the moisturizing factor wasn’t as long lasting as the coconut oil and olive oil.
  • One surprising fact that we uncovered is that natural coffee oil excreted when coffee beans were grinded was really moisturizing. Comparing the rose scrub to the coffee scrub, while both used the same amount of safflower oil, the coffee scrub actually leaves a softer, silkier feeling. And data supports this observation. This is something that we will continue to look into.
  • Conclusion –A blend of oils is definitely needed to achieve the right moisturizing factor and feel.

3.       Aroma – Data and Observations

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  • Only the Rose and Lavender Scrub used fragrance oil, and that results in general overall swoon from the panel of judges (aka us). Lemon scrub smells nice, but was lacking the depth and could benefit from some lemon essential oil. So will the grapefruit scrub. Oatmeal remains yummy due to coconut oil and molasses from brown sugar, but the consensus is that it could be tweaked to smell even more delicious, say addition of vanilla and cinnamon maybe.
  • One last thing we note was that coffee scrub is messy. Period. Coupled with the fact that I used the oldest, most oxidized coffee beans I have around, the resulting aroma is faintly (Or shall I say strongly?) reminiscent of burnt cigarette butts. No matter how much coconut and vanilla I added, it just simply wasn’t enough to mask the smell. And this is our first lesson on quality ingredients = quality products.

Plotting the averages onto a radar chart, and by looking at areas under each triangle, we found two clear winners – Oatmeal Brown Sugar and Rose & Lavender Sugar Scrub.

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We like Rose & Lavender Sugar Scrub because of a few factors – It smells awesome, thanks to the addition of rose fragrance. The fragrance lingered on for at least 5 hours after scrubbing. It delivered the right scrubbing consistency, had kaolin clay added which helped in softening the skin and safflower oil which is light and leaves virtually no greasy feeling. Most importantly, it had beautiful rose petals and lavender flowers added, making us feel extra pampered. The only drawback we found was the loose consistency. Having a loose powdery-like scrub means that it falls apart really easily, resulting in product waste down the drain. So my mission for this week is to figure out the correct Sugar : Clay : Oil ratio to get to a good scrub consistency.

We also like the Oatmeal Brown Sugar Scrub because it was gentle, and smelled SO YUMMY! Addition of coconut oil made the whole scrub smell like a yummy cookie dough. Oatmeal was gentle enough, but we feel like we could tweak the Sugar : Oat ratio to still deliver a gentle scrub that actually scrubs properly. We might need to explore a blend of white and brown sugar as brown sugar on its own doesn’t hold up well during scrubbing tests. We most definitely need to look into the oat size. We also liked the addition of coconut oil due to its moisturizing properties, but the scrub was simply too greasy. Overall, we need to relook into the Oat : Sugar : Oil ratio, or to create a blend of sugar and oil to keep the scrub gentle, and yet eliminate the greasy residue.

So, our mission for this week is to tweak these two scrubs. And that starts with a design of experiment (DOE). And maybe getting Brooke a food processor.

In the meantime, it’s time to find our guinea pigs, erm friends, buy them coffee, and get them mentally prepared for 30 mins of non-stop scrubbing action. Hey, that’s what friends are for, right? At the very least, they can claim their hands now glow in the dark. All thanks to The Soap Engineers! 😀


4 thoughts on “The Scrub Evaluation

  1. A college friend referred me to your blog. What fun! I will keep reading as I am able. Any blog with an ANOVA and such fun charts will be refreshing for me! I have a B.S. in Chemical Engineering, M.S. and Ph.D. degrees in Industrial Engineering, and work experience in semiconductors and the rubber industry. I’m using that background in creative ways as time allows as a stay-at-home mommy to three girls under 4. You can read some of my adventures at You may like my Oatmeal Scotchie experiment notes. Keep up the great (and fun!) work!

    1. Thanks for the encouraging words 🙂 We are really ‘nubes’ in this field so we thought we might as well approach this the engineering way. Which was surprisingly interesting because what we do at work literally applies to what we do for a new found hobby. And after reading your blog, it seems that we can apply the same engineering principles to almost everything we do – from cooking to cleaning. Which come to think of it, we do it sub consciously anyway. So we got to thank your college friend who introduced you to our blog, cos now we are introduced to yours 🙂 we’ll definitely post more as we explore more. We are officially making our first single oil soap tomorrow just to test out the properties.We’ll make a post on our observations for those soon. Can’t wait. And fingers crossed!

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