How to Avoid Soap Scum in the Shower

Reader Jenny says:

I have found my answer for the shower screen problem. Use liquid soap only in the shower. (Not my brilliance btw). It works really well!! The claim is that hard soap contains fat which causes scum.
Some general washing down still required of course for any mould buildup but no scrubbing, and now have clear screens. Whoopee!

This is an excellent idea!

I’ve discussed shower screens before. Essentially, soap scum is the calcium or magnesium salts of negatively charged surfactants.

As it happens there are four types of surfactants – anionic (negatively charged), cationic (positively charged), non-ionic (no charge) and amphoteric (both positive and negatively charged).

Each of these has its own particular applications, which is a story for another day, but the takeaway lesson for today is that by far the most common, and the cheapest, and the oldest, are the anionic surfactants (the ones that make soap scum).

Incidentally, when Jenny says they contain fat what she means is that they are made from fat ( and is easy to do at home – there is an idea for another post).

Liquid soaps on the other hand tend to be non-ionic in nature.  Therefore, none of the calcium or magnesium salts will form and no soap scum results.

Very clever!

If you want to use a hard soap, however, there is an option – Dove. I don’t know what’s in it, but I know it isn’t ordinary (anionic) soap, as it has a neutral pH (unlike anionic surfactants which are highly alkaline).

Dove is also available as an all over body wash, which is an excellent product which avoids those little unusable fragments of soap that you get in your soap holder when the bars get too small to use.

A Neat Detergent Trick

Some time ago I described the nature of detergents, with particular emphasis on a neat demonstration you can do.

Well, someone has come up with an even better one.

To reiterate what I said before, detergents are surfactants, which is an abbreviation of surface active agent – so any detergent loves surfaces, and this is why they clean dishes – they go looking for any interface they can find – liquid/solid or liquid/air. So when the tiny drop of detergent touches the surface it spreads out along the surface, pushing the pepper out of the way.

The Chemistry of Clothes Washing #10. Liquid Detergents

No discussion of laundry detergents is complete without discussing liquid detergents.

It’s probably fair to say that liquid laundry detergents play second fiddle to powdered detergents.  Having said that, this is probably based more on perception than performance, with many people thinking that when you buy a liquid detergent you are paying for a lot of water.

This is of course partially true, but not to the degree you may think.  Whereas dishwashing detergents are between 80 to 90% water in general, laundry detergents are typically around 50 to 60%.

Liquid detergents generally use non-ionic surfactants rather than anionic surfactants, which doesn’t mean much in terms of cleaning other than that they tend to be a little more versatile in terms of their stain removal properties.

The two standout performers in terms of liquids are Dynamo and BioZet, for different reasons.  Whereas the BioZet (which also comes in a powder) is a largely enzyme-based product, the Dynamo is a very sophisticated formula where they have managed to suspend material in the liquid that is not normally liquid soluble, which gives the liquid an opaque appearance.  Technically, this makes it a suspension rather than a solution, but let’s not go into that for now.

Specifically, Dynamo has managed to suspend perborate and percarbonates materials in their (laundry bleaches), as well as adding a sophisticated enzyme matrix.

Also, liquids have the advantage of providing a prewash capability.  That is, if you had a particular stain, you would just rub a bit of the liquid into the stain before putting it in the wash.  If you tried the same thing with a powdered detergent, you would get fluorescent burns in the material (from the fluorescing agents).

And, of course, you do not need to worry about solubility of the liquids, so they are certainly a good option for cold water washing, if that’s what you wanted to do.

Another interesting market trend that has occurred in recent years is that for many of the brands on the market, they are available as both liquid and powder, which did not used to be the way things were.  It used to be the case that if you wanted a powder you bought one brand and if you wanted a liquid you bought another brand.

Oh, and here’s a final tip if you are using liquids.  One of the most annoying things about liquid detergents is that if you use the cap to measure out the liquid, then it makes a mess when you put it back on the bottle.  A simple solution that I have used when I have used liquids is that you simply toss the lid in with the wash.  Retrieve it afterwards, and it’s nice and clean so it doesn’t make a mess when you put it back on the bottle.

Okay, tomorrow I will summarise things and go through a few common mistakes that people make.  Then we’ll start looking at pre-washes.


Washing Dishes Without Detergent.

Incredible but true! in fact it works so well that you don’t even need to use a scourer.

Here’s how it works.

Anything that is water soluble will just rinse straight off with water.  That just leaves you with the oils and fats from the food.

There are two ways to attack this:

Firstly, use a detergent.  The detergent molecules wrapped themselves around the fat, form themselves into micelles, and then the water can carry them away.

The second approach is to use an alkaline substance to convert the oils and fats into soaps.  And this of course is how soap is made – you react fat with caustic soda.

So it’s simple.  Run some hot water into the sink, and as you do it throw in some washing soda – a heaped tablespoon should be plenty.  Now, just let it soak for about half an hour, so that it cools down a bit.  Now, just lift the plates out, rinse them under cold water, and Bob’s your uncle.

You will be amazed at how well it works.

By the way, the same approach will work with detergent, although not as well.  Letting the dishes soak in hot water for half an hour allows the detergent molecules to do their stuff.  The thing that separates the detergent from the washing soda is baked on cheese (e.g. from nachos) for which the washing soda leaves detergent in its wake.

Suds and Fizzing

We associate suds with cleaning. This also extends to fizzing.

When you add Harpic toilet cleaner to the water in your bowl, we think it it working because it is fizzing.

Actually, it fizzes because the bisulphate is reacting with the carbonates – it is fizz for fizzes sake – nothing to do with cleaning.

The same is true of the popular home recipe of adding bicarb to vinegar. All it is, is fizzzing for the sake of fizzing.

In fact the bicarb and vinegar are neutralising each other. Here’s the reaction:


The gas that’s coming off is carbon dioxide, and has no cleaing power whatever.

Hair shampoos have foaming agents added to them, which is necessary as the (amphoteric) surfactants that make up many hair shampoos are low foaming, and may create the impression of poor cleaning if they didn’t foam.

Yet another case of “perception is reality” in the marketing of household products.