The Alum Block: What It Does After a Shave and How to Use It
An alum block is a smooth bar of mineral salt, usually potassium alum, that you glide over wet skin after shaving. It is an astringent: it tightens the surface of the skin and helps tiny nicks and weepers stop bleeding. It also gives you feedback. Where it stings, you have irritated the skin with too much pressure, too many passes, or shaving against the grain, so it quietly shows you where your technique needs work. Use it on a clean, freshly rinsed face, leave it for about a minute, rinse it off, then moisturise. It is cheap, lasts a long time, and it is not a substitute for a balm.
Here is how it works in practice, how to use it, and when to leave it in the cupboard.
What an alum block is
Alum is a naturally occurring mineral salt that has been used in shaving for a very long time. The block is a solid, translucent piece of it, cut and polished into a bar that fits in the palm. Most are potassium alum; some are ammonium alum. Either works in the same way.
It is sold in a small box, often with a lid, because the block slowly dissolves in water and needs to dry between uses. One block can last for a long time with daily use.
What it does on the skin
It is an astringent
Alum causes the surface of the skin to tighten slightly. That is what you feel as a faint drawing sensation after using it, and what gives the face a fresh, firm feel straight after a shave.
It helps small nicks stop bleeding
The same tightening effect helps stop the small pinprick bleeds that often follow a close shave. It works on weepers and tiny nicks, not on a proper cut. For anything that keeps bleeding, press a clean tissue or cloth on it for several minutes. Our guide to stopping a shaving cut from bleeding covers what to do. For any deeper cut, the NHS guidance on cuts and grazes explains how to clean it and when to get help.
It tells you how well you shaved
This is the most useful part, and the reason many experienced wet shavers keep one. On skin that you shaved gently, an alum block barely tingles. On skin that you scraped, pressed or went over too many times, it stings. Over a few weeks, the pattern tells you exactly where to change your technique, which is usually the neck, the upper lip and under the jaw.
How to use an alum block, step by step
- Finish shaving and rinse your face with cool water to remove all the lather.
- Run the block briefly under cold water to wet the surface.
- Glide it gently over the shaved area. No pressure is needed; one pass is enough.
- Pay attention to where it stings. Make a mental note.
- Leave it on the skin for around 30 seconds to a minute.
- Rinse your face with cool water. Alum left on the skin can feel tight and drying.
- Pat dry and apply a balm or moisturiser.
- Rinse the block, shake off excess water, and leave it to dry completely, out of its box, before you put it away.
Alum block, styptic pencil or balm?
These three do different jobs, and they are easily confused.
| Product | What it is for | How you use it |
|---|---|---|
| Alum block | Whole-face astringent, small weepers, technique feedback | Glide over the whole shaved area after rinsing |
| Styptic pencil | Stopping a specific small nick | Wet the tip and press it on the nick only |
| Aftershave balm | Soothing and moisturising | Apply after rinsing off the alum |
A styptic pencil is more concentrated, so it is better for an individual nick, but it stings more. An alum block is gentler and covers the whole area. A balm is the last step. If you are deciding what to use at the end of a shave, our guides to aftershave balm vs splash and witch hazel after shaving cover the other options.
When not to use one
- On very dry or sensitive skin, every day. Alum is drying. Use it occasionally or only on nicks.
- On broken, inflamed or infected skin, such as a rash, eczema flare or bumps that are sore or weeping.
- On a deep cut. It is for tiny bleeds only.
- If it causes a rash or ongoing redness. Stop using it. If you are prone to skin reactions, try it on a small area of your jaw first.
Looking after the block
Alum dissolves slowly in water, so the main enemy is damp. Always let it dry fully before closing the box, otherwise it becomes slimy and wears away more quickly. Keep it away from where it could be knocked off a shelf: it is a crystal, and it can chip or crack if dropped. A chipped block still works, but rough edges can scratch, so smooth them by rubbing under water or replace it. Do not share it; it touches freshly shaved skin.
Is it worth buying one?
If you wet shave with a safety razor, a straight razor or even a cartridge, and you get small weepers or irritation, an alum block is one of the most useful and inexpensive things you can add. If you shave with an electric shaver or only use a trimmer, you are unlikely to need one.
The bigger gains usually come from technique: prep, a sharp blade, shaving with the grain and light pressure. Our step-by-step guide to shaving properly is the place to start.
Seeing a proper shave done
Watching an experienced barber shave you is a quick way to learn what good technique feels like. A hot towel shave at our barbers on Archway Road takes 20 to 30 minutes, and every visit starts with an assessment of your skin and hair, so you can ask about your own routine and aftercare while you are there. To book, contact the Highgate Cuts team by email.
Questions we get asked
Why does my alum block sting?
It stings where the skin has been irritated by shaving, often from pressure, extra passes or going against the grain. It is a useful sign of where to be gentler.
Do you rinse off an alum block?
Yes. Leave it for about a minute, then rinse with cool water and moisturise, as alum left on the skin can be drying.
Is an alum block the same as a styptic pencil?
They work in a similar way, but a styptic pencil is more concentrated and meant for individual nicks, whereas a block is used over the whole shaved area.
How long does an alum block last?
A long time, often well over a year with regular use, provided you let it dry properly between shaves.
Book with The Highgate House
Ready for a proper cut? Email us at [email protected] with the service and the day that suits you, and we will come back to you with times.
Visit The Highgate House · The barbers
The Highgate House, Archway Road, Highgate, London N6.
