Salt Spew

Salt Spues and Fatty Blooms

Gasp! Shock! Horror! Have you ever opened a brand new box of leather shoes or boots, which you purchased a few months ago – only to find what looks like a white mould on the leather upper? Either in a small amoeba like pattern or streaky lines? You need not panic nor throw a tantrum. Not everything located on the surface of your leather footwear is mould. In fact, in the case of a FMCG like safety footwear – 99.9% of the time you are in fact dealing with oils or salts migrating from within the leather and crystalising on the surface. It is quite a common occurence.

Is this mould on my leather boots?

To distinguish the one from the other, we must rule out the obvious. If you have turned your beautiful leather boots into gumboots and paraded around in knee deep water all day, and then tossed them into a damp and cold environment for a week or two… and they start to smell – then yes, your boots (leather is a natural material, a deceased animal skin!) probably smell like mildew and you have a fungus or bacteria growing on the leather. (Like a piece of old white bread, this growth will be far larger spread, thicker and green/yellow in colour. But, the smell will be the giveaway.) This is mould. And you should have taken more care of your expensive leather safety boots.

What is a Salt Spue or a Fatty Bloom?

But, if this new pair of boots hasn’t been near moisture and are indeed brand new (and all you smell is that beautiful, rich, natural leather aroma) then you are most certainly dealing with a Salt Spue or a Fatty Bloom. If you have stored your new purchase for a while, wanting to get your last few kilometres or even months out of your last pair, you may be met with this white substance. You have nothing to fear. It is a direct result of the fats, oils and waxes used during the tanning process. And happens due to either a rapid temperature shift (hot to cold / or vice versa as we experience in seasonal changes) or high humidity – these salts, oils and waxes move to the surface. They migrate through the layers in the leather skin (leather upper), and crystalise upon the exposed surface.

It can happen to any type of tanned, oily leather product; wallets, shoes, jackets, pants and even belts. It is not harmful to the product at all, but unfortunately doesn’t look aesthetically pleasing – immediately resulting in the purchase being deemed bad quality or returned. This is not the case.

We often show our clients that it is salt, but touching the small “pinky” finger to the tongue and then touching the spue, and touching the tongue again. Often the salt can be detected in taste. But, you don’t need to be a detective or private investigator to fix the issue. It is very simple to remove and resolve.

How To Clean Salt Spue from Leather Boots?

The boots are new, so firstly you could rub them down (like when polishing) with a dry cloth or small towel (even the branded ProFit fabric wrapping inside the box works). The rubbing resistance, and heat, will start to remove the white and the spue or bloom will disappear. If you have some time on your hands, and the weather is suitable – place them inside a comfortable warm or heated room or even in the sunlight. Natural warmth will cause the spue to disappear as it is drawn back into the leather and dries. But NEVER place the boots or shoes next to a direct heat source like a fire place, nor try and speed dry on a heater or with a hot hair-dryer. You will damage the leather. Natural sunlight or warmth is the best option. Then give the product a good polish with a commercially available shoe polish (Plush, Lion, Kiwi, Nugget, etc) or a bees wax or dubbin, or even a leather food or leather oil.


Walking through small puddles of water or being caught in a rain downpour often wets the leather uppers as well, and one can see lines appearing around the shoe or boot where the height of the water reached. This is again an example of the salts used during the tanning process coming towards the surface. It can even happen on a very hot day where you have been very sweaty, or sweated a great deal inside your footwear. (Commonly seen on the area of a leather belt which sits in the middle of your back!) But a simple, good polish will remove these natural tanning agents. And polishing always means maintenance, longevity and a longer lifespan for your boots or shoes. It’s a win-win scenario.


We never stop learning! Talk to the professionals at ProFit Safety Footwear for more helpful hints and tips on understandinhg leather and safety footwear. We are at your service.