Have you ever bought yourself a face scrub and wondered how long those lovely scrubby bits and pieces will stay suspended in their gel or cream home?   Maybe you are a wannabe or actual scrub maker wanting to know how long your particular brand of loveliness will remain nice and tidy on the shelf?  Maybe you just don’t give a damn but have nothing better to do for the next 5 minutes of your life.

Well you guys are in luck as I’m going to let you into my secret world of stability testing starting with method validation.

Facial scrubs can come in all different shapes and sizes but are most commonly either in a cream or a gel base.  Cream scrubs start off life as a normalish moisturiser to which something bubbly and then something scrubby are added.

Gels start off life-like a typical hair gel and also get pimped with a little something bubbly then scrubby.

Both can be just as rough or mild with creams winning out for ultra-dry skin due to their inbuilt oil phase.

As many a cosmetic chemist will tell you the problem with facial scrubs is keeping the scrubby bits suspended – fighting gravity.  This can be achieved in a number of ways including matching the density of the scrub particle with the base (pretend that the two are weight lifters, they need to both be the same grade),  making the continuous phase (usually water) thicker and harder to ‘move through’ (try to visualise your scrub particles running through water, then custard, then thick toffee….).  Finally and most importantly are suspending agents which act like spiders webs by structuring the continuous phase (water) like a net, preventing your scrubby stuff from falling straight through it.

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