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How To Use An Alum Block After Shaving

Alum is a wet shaver’s go-to for calming down razor burn and stopping cuts from bleeding. Here’s everything you need to know about how to use an alum block for those painful post-shave moments. 

Table of Contents

What Is An Alum Block And What Is It Made Of?

Alum block is an incredibly popular wet shaving remedy for post-shave cuts and irritation. Some men like to use it all over their face, like an aftershave, while others only use it on spots where they’ve accidentally nicked themselves.

At first glance, an alum block looks like a solid piece of slightly-transparent rock. It could just as easily be a block of salt. In a way, it sort of is a salt – the metallic, acidic kind instead of the type you’d have on your dinner table. Alum blocks are usually made of potassium alum, which is the double sulfate of potassium and aluminum. Occasionally you’ll find options made of slightly different compounds. 

Alum acts as a powerful astringent and antiseptic. Astringents, if you’re not familiar, are materials that can cause tissue to constrict. 

Have you ever had that tight feeling in your mouth after drinking a very dry wine or biting into an unripe fruit? That’s astringency! When applied to the skin, astringents make it feel tight. Their effect helps to tame inflammation by reducing swelling and redness.  

There are a lot of astringents in the grooming world (especially as aftershaves and toners), but alum blocks take it up a notch. They’re very powerful, so they don’t just constrict the skin to reduce redness and razor burn, but they can actually help stop bleeding from minor cuts.

As for antiseptic, this means that alum helps to kill off bacteria that might lead to skin infections like folliculitis. The winning combination of astringent and antiseptic make it a wonderful preventative for razor bumps.

Because alum is acidic when mixed with water, it will sting any parts of your skin that are a little more irritated. Some men like to rub it all over their face, as a way of checking for irritation and figuring out if they did a good job with their shave. 

Alum Block vs Styptic Pencil

Alum blocks and styptic pencils are usually the same material but packaged differently. Choosing between one or the other is mostly a question of convenience and price, so here’s the basic breakdown. 

  • An alum block is just a big chunk of alum, while styptic pencils are alum (or similar materials like aluminum sulfate) shaped into a thin cylinder and mounted on a plastic base, with a cover. 
  • A large alum block costs about the same as a small styptic pencil, so if you’re strictly judging based on quantity, alum blocks offer the better bang for your buck.
  • If you’re looking for something you can rub all over your face after shaving, an alum block is an obvious choice. You can apply it to your entire face in seconds – something that isn’t possible with a styptic pencil. 
  • Styptic pencils tend to deposit more alum when you rub them over the skin, so they’re better for deeper cuts. 
  • Because of the smaller size, styptic pencils are a little more convenient if you’re only spot-treating small areas, but not by much.

How To Use An Alum Block

Use the alum block after you’ve finished shaving and rinsed away any shaving cream residue.

  1. After shaving, splash your face with a healthy amount of cool water, so it’s slightly damp. 
  2. Rub the block over the areas that need to be treated, whether it’s all-over or only on specific spots. 
  3. If you don’t feel like any alum is coming off on your skin, you may want to dampen the block directly, although doing this regularly can cause the block to lose some of its smoothness. 
  4. If you only have a couple of small cuts you want to seal, only dampen a small corner of the block, and rub that over your skin.  
  5. Let the alum sit on your skin for around 15-20 seconds at the very least (some shavers prefer to leave it for a few minutes), until bleeding and irritation go down. 
  6. Rinse off the alum with more cool water. 
  7. Alum can leave your skin dry, so finish off your post-shave routine with an aftershave balm or moisturizer. 
  8. Finally, make sure to dry the alum block with a towel, and leave it somewhere clean to dry. 

Can You Use An Alum Block Everyday?

Alum is potent stuff, so not everyone can use it every day. I recommend easing your way into it. After the first time you use it, wait a few days and see how your skin reacts. 

If all is well, you can try using it for a couple of days in a row. If you don’t notice any signs of irritation, you can use it every day. On the other hand, if you find that it does slightly irritate your skin with repeated use, you may want to only use it when highly necessary. 

How Long Should You Use Your Alum Block?

Here’s a quick rundown of alum block timing: 

  •  Leave it on your skin for a few minutes or less once you finish shaving. 
  • Many wet shavers use it every day with good results, but others find it irritating. To figure out how often you need to use it, introduce it slowly and close pay attention to signs of stinging or redness.
  • Alum blocks don’t expire, so you can use yours for as long as it feels smooth on your skin. 

Should I Wash Off My Alum Block?

Probably. Alum is a powerful astringent and it does its job quickly. There aren’t any benefits for leaving it on any longer, but you risk irritating the skin, which is counter-productive. 

Oh, and that layer of invisible alum block on your skin isn’t necessarily going to stay undetectable, which is another reason to rinse it off. If you leave it on, you may find white, powdery patches on areas where you went a little heavier with the alum. It can also clump up and become visible if you follow it up with aftershaves. 

It also has a sour metallic flavor that you don’t want to accidentally taste when you lick your lips. Your romantic partners probably won’t appreciate it, either. 

All that said, there are guys who find they get great results and no irritation or white patches even when they leave the alum on their skin. If leaving it on works for you and doesn’t cause issues, who am I to tell you to do otherwise? 

How Long Does Alum Block Last?

Alum blocks don’t expire, but they can lose their smoothness or harden to the point where they’re difficult to rub over the skin. If you’re diligent about keeping your alum block dry these issues won’t crop up, and it’ll easily last you for years and years of shaving even with daily use.

Does Alum Stop Hair Growth?

No. There’s a myth that alum will slow down hair regrowth, but it’s largely spread by pseudoscientific DIY recipe articles that prey on insecure women. It’s not based on any science or research. As hundreds of thousands of men who’ve been using it for decades can attest, their facial hair is still growing at the exact same rate. 

Other Uses Of Alum Blocks

There are a lot of ways to use alum, so here’s how you can get more utility out of your block. 

Antiperspirant: Your alum block can also be a great deodorant. The active ingredients in commercial antiperspirants are all aluminum-based, much like an alum block. When left on the skin, that layer of powder helps to block the sweat glands to prevent sweating and bad odors very effectively. To use alum as an antiperspirant, dampen your block and then rub it under your armpits as you would a regular deodorant.

Acne treatment: A lot of men notice that they break out less often once they start using an alum block in their shaving routine. Its constricting effects make it a great ingredient for bringing down red, painful pimples, while the antiseptic effects prevent infection in the first place. You can use it as a spot treatment or even as a preventative face mask. 

Post-waxing: Waxing is even more irritating than shaving since it pulls hair straight out of the hair follicle. If you wax, use alum afterward just as you would for shaving. It can help prevent or reduce redness, irritation, and bumps.
Bug bites: Itchy bug bites got you down? Your alum block can come to the rescue yet again! In a pinch, rubbing a little bit of alum over a bug bite can give some relief against the swelling and itching.

Miles is a professional men's grooming analyst who believes that to look good a man just needs to take good care of himself. He’s all about wet shaving, sustainability, and evidence-based grooming - an obsession he’s ready to share. Miles is known for his in-depth analysis of men's grooming products, brands, and best practices you can't find anywhere else.