Keratin or creatine: which one is the gym supplement?

If you searched for "keratina gym", this is what you were after

It happens every day. Someone overhears in the changing room that you should take "keratina", types it into a search engine as it sounds and ends up reading about Brazilian blowouts. The two words sound alike, are spelt almost the same and, in Spanish, keratin even has two spellings in circulation, so the mix-up is easy.

To the point: the white tub on the gym shelf is creatine. Keratin is something else entirely: it lives in your hair and is not sold for training. And there is a third word lurking, creatinine, a waste product your kidneys remove that shows up in blood tests.

This page exists to clear up the doubt in thirty seconds. If you already know the answer and want the instruction manual (exact dose by body weight, loading phase, types of creatine, when to take it), you will find all of it in how much creatine to take a day and how.

Creatinine deserves half a paragraph, because it completes the triangle. It is the waste product left when muscle uses creatine, and the kidneys clear it in the urine. That is why it appears in any routine blood test. You do not buy it or take it: it is a marker. If someone talks about "creatinine levels", they mean your medical report, not your tub.

Is it keratin or creatine?

They are two different words, not two ways of spelling the same thing. Creatine is the compound you take at the gym. Keratin, which Spanish writes queratina or keratina, is the protein in hair and nails. If you were after the tub from the gym, your word is creatine.

The mix-up starts with sound. Say ker-a-tin and cre-a-tine out loud and they are close enough for the brain to fill the gap with whichever it has heard more often. In Spanish it is worse, because hairdressing products and science papers both use keratina, copied from English, alongside the standard queratina.

Add that both are loosely thought of as "protein" (creatine is not one; it is a compound derived from amino acids) and you have the perfect combination. "Keratina gym" is in fact a running joke on social media in Spain precisely because it happens to so many people.

What is "gym keratin"?

It does not exist: what sports nutrition shops sell is creatine. Keratin is a structural protein of hair, nails and skin, and it is not marketed as a performance supplement. When someone says gym keratin they mean creatine.

If you ever see a product advertised literally as "keratin for the gym" at a suspiciously low price, be wary. Either it is a badly translated creatine label, or it is a hair supplement sold where it does not belong.

What keratin really is

Keratin is a structural fibrous protein. According to the medical dictionary of the Clínica Universidad de Navarra, it is found in the outermost layer of the skin, in hair and in nails, and is responsible for their strength and durability. It also appears in the epithelia lining internal structures.

The Cleveland Clinic says the human body has 54 different keratins, split into two families (type I and type II). It is a whole family of proteins that your body makes for one very specific purpose: to give firmness and protection to the tissues in contact with the outside world.

What makes it so tough is its composition: plenty of cysteine, an amino acid containing sulphur. Those sulphur atoms bond to each other to form disulphide bridges, which turn a heap of amino acids into something as hard as a nail. It is exactly what a keratin hair treatment breaks and rebuilds at the salon.

Here it is worth separating two things that share a name. One is the hair treatment: a product applied to the hair, at the salon or at home, that works from the outside. The other is the oral supplement, a capsule or powder you swallow. That both carry the word keratin on the label does not mean they do the same thing or have the same amount of evidence behind them.

What does keratin do in the body?

Keratin is a fibrous protein that forms the outer layer of the skin, the hair and the nails, and gives them hardness and durability. It is rich in cysteine, an amino acid containing sulphur whose bonds make it hard and stable. Your body makes it on its own.

Which foods contain keratin?

None in a directly usable form: the keratin in a food is digested into amino acids like any other protein. What eggs, fish, meat, dairy and pulses do provide is the cysteine and methionine your body uses to make its own.

This is a secondary confusion worth clearing up, because plenty of lists of "keratin-rich foods" circulate. No food passes intact keratin to your hair: your digestive system breaks it down just as it breaks down meat or eggs. What you can look after is the supply of raw material.

• Egg: provides cysteine and methionine, the two reference sulphur amino acids.
• Fish and meat: complete protein, and they are also the natural dietary source of creatine.
• Dairy and pulses: top up your daily protein without complicating the shopping.

What is a keratin supplement for?

It is sold in the beauty category, for hair, skin and nails, almost always as hydrolysed keratin. The evidence is thin and comes from small trials. The Cleveland Clinic points out that no studies conclude that these supplements strengthen hair.

It is worth being straight about the data. There is a randomised, double-blind, placebo-controlled trial (Beer et al., 2014) in which 50 women took a soluble hydrolysed keratin with vitamins and minerals for 90 days, and the active group improved against placebo on several hair and nail measures. It is a well-designed study, but small, women only and tied to one commercial ingredient. A single piece like that does not make a firm recommendation, which is why sources such as the Cleveland Clinic still say no studies conclude that these supplements strengthen hair.

In short: keratin has some evidence, though thin, and it was not what you were after when you typed "keratina gym".

Keratin and creatine, side by side

Here are the two, row by row. If you read only one thing in this article, make it this table.

The second-to-last row settles the debate. Creatine is the only one of the two that a label can say improves performance, and only if it provides 3 g a day. Nothing about training can be said of keratin.

What happens if you take keratin expecting creatine results

First, reassurance: you will not hurt yourself. Second, and less pleasant: you will throw away money and several weeks of expectation. You will be taking a product designed for another tissue and another consumer category, while the training effect you expected never arrives.

The hidden cost is time. Plenty of people try it for three months, notice nothing and conclude that "supplements don't work", when what happened is that they bought the wrong tub.

There is an even more common variant that never reaches the checkout: someone searches "keratin for the gym", sees hairdressing results, gets confused and drops the idea. They are left thinking that what they were told about does not exist. It does, and it is called creatine.

A third scenario: buying keratin in the belief that it will do both jobs. Here the problem lies in the expectation. A beauty supplement is judged by beauty criteria, and there is no biological reason for the protein that stiffens a nail to affect how you lift a bar.

Which is better for the gym, keratin or creatine?

For the gym the answer is creatine, and the two do not really compete. Creatine is the only one of the two that a label can say improves performance, and only at 3 g a day. Nothing can be said of keratin about physical performance.

Does keratin for the gym have side effects?

There is no keratin for the gym: that product does not exist in sports nutrition. The keratin supplements sold for hair are considered well tolerated in the studies available, although there are few. If you want performance, the product you were after was creatine.

There is little to add on safety because little has been studied. The trials available with hydrolysed keratin reported no relevant problems, but they are few and short. If you have a health condition or take medication, the conversation is with your doctor or pharmacist, not with an article.

Right, it was creatine: where to go next

Now that you have the right name, the next step is working out which format suits you. We will not repeat here what is already covered elsewhere: the dose by body weight, whether you need a loading phase, how monohydrate, Creapure, micronised and HCL differ, and what to expect week by week are all explained in detail in the guide to creatine for the gym.

And if the doubt you are left with is the other classic from the changing room, creatine or protein, it is settled in creatine vs protein: differences and when to take each.

Can you buy keratin for the gym?

Not in a sports nutrition shop, because it is not made for that use. What you will find is creatine, as plain monohydrate, flavoured, in a pack or combined with protein. Keratin is sold in pharmacies and perfumeries, in the beauty section.

Is there keratin powder for the gym?

The white powder in the gym tub is creatine monohydrate, not keratin. It comes as a powder because that mixes with water and is measured with a scoop. If you see keratin powder advertised for training, it is either a labelling error or marketing.

A practical note on formats, since this is where most people get stuck when they reach the shop with the word they have just learnt:

• Plain monohydrate: the reference format, unflavoured, to mix with water or whatever you already drink.
• Flavoured: the same idea, easier to take every day if the plain one is a struggle.
• Creapure: a monohydrate brand with documented purity control.
• Combined: inside a protein blend, in a bar or in an all-in-one with magnesium and collagen.
• In a pack: if you already know you will use it continuously and want to restock without thinking.

All the formats are in the creatine category, and below you have a concrete selection.

The trick to never mixing them up again

The C of creatine is the C of body: muscle, training, a tub of white powder. The K of keratin is the K of hair, nails and skin, and it sits in the beauty section. Creatinine, with its extra syllable, is not something you buy: it turns up in the blood test.

And if in a month you doubt again, here is an even shorter rule: if you heard the word at the gym, it is creatine. If you heard it at the hairdresser's, it is keratin.