Truthfully, there’s no sure way of knowing exactly when castile soap was invented. Soap is mentioned in the Old Testament, but they didn’t wax on about what kind of soap it was. Today, our best guess is that Castile soap originated in Aleppo, Syria. It’s rumored that Egyptian royalty, including Cleopatra, used it for bathing, but that’s difficult to substantiate as well.
What’s so great about castile? For one, it’s plant-based. Other soaps are traditionally made with lard or tallow, which are just alternate words for animal fat. ‘Tallow’ typically means it came from a cow, while ‘lard’ is commonly used to describe pig fat.
On one hand, it makes sense to avoid tallow-based soaps for ethical reasons. But these soaps do make use of byproducts from the meat industry that would otherwise be wasted, making it a relatively green practice.
Soaps containing animal fats also harden much easier. Castile soaps take time to set and often require aging afterward. But as they say, good things are worth the wait.
As to what plant oils should actually be used to make castile soap, there’s a bit of a debate. Traditionalists will proclaim that castile soap is made with only olive oil. But as times have changed, soap making has spread far and wide beyond areas where olive groves are easily accessible.
Still, there are those that maintain that ‘castile’ is synonymous with ‘olive oil soap’. But in the Castile region of Spain, where this soap allegedly got its name, olives were plentiful, vital to industry and agriculture. That original recipe the Spanish adapted from the soap makers of Aleppo probably didn’t contain only olive oil, either. It’s said that they used laurel berry oil as well.
These days, we can interpret ‘castile soap’ as a term that describes soap made with plant oils, as it is used to clearly differentiate the ingredients from that of soap made with animal fat.
Is there a difference between bars and liquid? Yes, and it’s in the processing. Liquid castile goes through saponification using potassium hydroxide, and bar castile soap requires lye to saponify. Don’t worry - these do not remain in the soap. For this reason, it’s not listed on most ingredient labels.
If you’re very familiar with castile soap, you’ve probably tried the ubiquitous fair-trade brand in liquid form. While bars are more familiar to many of us, liquid castile highlights another great benefit to choosing castile soap: it’s very multipurpose and can be used to wash, well, pretty much anything.
Real castile soap can be used to wash dishes, laundry, floors, walls, and much more. The only rule is that you can’t add acids, like vinegar and lemon juice, to clean. These can reverse the saponification and make the soap oil again. Sounds only slightly more appealing than scrubbing everything you own with animal fat, doesn’t it?
Castile soap is also typically much gentler than fatty soaps, making it more well-tolerated by sensitive skin types. However, some companies will still add unnecessary ingredients to castile soap, so you still have to check labels.
Ideally, your soap will only contain saponified oils, with the addition of some herbs or essential oils for extra benefits. Gentle, inexpensive, and free of animal products, castile soap is the all-natural way to get clean.