Anyone who has used an anaesthetic cream, insulin patch or nicotine patch will attest to the ability of chemicals to be absorbed into the body through the skin. The principle is used in medical applications all the time.

Clearly it's not a good idea to have all manner of environmental substances entering your body in this way and nature has provided us with a barrier defence against that and it's called sebum. Sebum is the very thin layer of oil you find on your skin, which – as well helping to keep out bacteria – also helps keep your skin moisturised.

Many cleaning agents used in industrially manufactured soaps are very efficient removing oil of all kinds – unwanted as well as wanted. That's why many soaps leave your skin feeling dry and in need of something. Sometimes, multiple somethings.

Castile soap – made from olive oil – preserves this protective layer and you can really feel the difference when you use it. While olive oil doesn't quite grow on trees, it's about as close to it as you could hope for, and given its natural ingredients and 800 years of use, animal testing is unnecessary and therefore cruelty-free.

Perhaps its greatest long-term property is that it's biodegradable, meaning that even if it does find its way into the sea or water courses, it's not going to persist there and will be broken down by bacteria.