AMINO ACID
Citrulline
- amino acid
An amino acid used in conditioning blends for moisture binding.
- products in our library
- 10
- of researched products
- 0.1%
- on the label, in our conditioners
- usually #41
- most common in
- Conditioner
- in water
- Water-soluble
At a glance
Four things worth knowing about how this ingredient behaves on hair.
How much of it is left on hair between washes.
What it takes to get it off the hair again.
Smaller fragments travel further into the strand.
Read from where it sits on the labels we have, not from the molecule.
| Property | Level | Out of |
|---|---|---|
| Buildup risk | Low | 1 of 5 |
| Rinse-out behaviour | Rinses clean | 5 of 5 |
| Fragment size | Smallest | 1 of 5 |
| Stiffening potential | Slight | 2 of 5 |
What it does for a formula
What Citrulline does
The general function first, then how the role changes by product type where we have researched it.
Small enough to travel further into the strand than a whole protein can.
Water alone removes it, so it does not accumulate between washes.
Charge
Charge is not recorded for this ingredient.
Solubility
Rinses out with water alone, so it does not build up on hair between washes.
Where it appears
Where it appears
One row per product category in our library: how many products list it, what share of that category that is, and where it typically sits on the label.
| Product type | How common | Typical position on label ? |
|---|---|---|
Conditioner
2 products
|
secondary · #41 | |
Mask / treatment
2 products
|
secondary · #54 | |
Shampoo
2 products
|
secondary · #56 | |
Leave-in
1 product
|
secondary · #32 | |
Scalp treatment
1 product
|
secondary · #44 | |
Styler: mousse
1 product
|
secondary · #23 | |
Styler: paste
1 product
|
secondary · #29 |
| Product type | Products | Share of category | Median position | Earliest position | Band |
|---|---|---|---|---|---|
| Conditioner | 2 | 0% | 41 | 32 | secondary |
| Mask / treatment | 2 | 0% | 54 | 34 | secondary |
| Shampoo | 2 | 0% | 56 | 36 | secondary |
| Leave-in | 1 | 0% | 32 | 32 | secondary |
| Scalp treatment | 1 | 0% | 44 | 44 | secondary |
| Styler: mousse | 1 | 0% | 23 | 23 | secondary |
| Styler: paste | 1 | 1% | 29 | 29 | secondary |
We have not researched differences by product type yet. The reading below comes from where it sits on the labels in our library.
Position footprint
Every listing in our library, by position on the label.
| Positions | Zone | Listings |
|---|---|---|
| 1-3 | Leading | 0 |
| 4-8 | Supporting | 0 |
| 9-15 | Secondary | 0 |
| 16-25 | Lower | 1 |
| 26+ | Trace | 9 |
How to read this
US labelling rules put ingredients above 1% in descending order of amount; below 1% they may be listed in any order.
So position tells you about relative amount only above that line, and we never convert a position into a percentage.
Who should pay attention
Formulation guidance for specific hair conditions, limited to the label positions where it applies. It is not a conclusion about any finished product, or about you.
Amino acids are the smallest protein fraction and bind water as well, so they add far less stiffness than a hydrolysed protein does.
The lightest option in the protein family, but still protein — worth watching if protein reliably stiffens your hair.
Read from this ingredient’s chemical class. Where we have researched the ingredient itself, that reading replaces the class one.
Why it matters to shoppers
What seeing this ingredient tells you, what it does not, and the limits of our own method.
- the lightest protein option
- a light protein
- a rinse-clean feel
- help on very dry or damaged hair
- an exact safety score (we do not publish one for any ingredient)
- how a finished product performs, which depends on the whole formula, not one line of it
- the exact percentage in a bottle, because label position never converts into a number
- a secondary amino acid, listed below the main ingredients in our conditioners
- it was on the printed ingredient list of every product we counted (we read labels, not marketing copy)
- that a product is right or wrong for you
We do not publish safety scores or hazard grades. Where a regulator has published a restriction or a use condition, we state it and cite it; otherwise we describe what the ingredient does and stop.
Commonly paired with
The ingredients that most often appear alongside this one in our library. We leave out the near-universal ones, because they pair with everything and tell you nothing.
- Caprylyl Glycol · 10
- Ethylhexylglycerin · 9
- Niacinamide · 7
- Biotin · 7
- Glucosamine HCl · 6
- Hydrolyzed Soy Protein · 6
- Sorbic Acid · 6
- Pentylene Glycol · 6
- Propanediol · 6
- Glucose · 5
The number beside a name is how many products in our library list both.
These ingredients tend to appear together to hold on to water, soften the strand, and improve feel after rinsing.
Found in these products
The most prominent placements first. The badge is the position on that product’s own ingredient list.
Grande Cosmetics · Styler
GrandeHAIR Full Boost Volumizing Foam
#23 on the label · $5.13/oz
R+Co · Styler
MANNEQUIN Styling Paste
#29 on the label · $6.20/oz
Bondi Boost · Conditioner
BOND BUILDER+ CONDITIONER
#32 on the label · $1.86/oz
Bondi Boost · Leave-in
Strawberry Gum Miracle Mist Leave-In Conditioner + Heat Protect
#32 on the label · $6.31/oz
Bondi Boost · Mask / treatment
Bond Builder+ Hair Mask
#34 on the label · $3.91/oz
Bondi Boost · Shampoo
BOND BUILDER+ SHAMPOO
#36 on the label · $1.86/oz
Pura d'or · Scalp treatment
Advanced Peptide Hair and Scalp Serum Hair Regrowth Tonic
#44 on the label · $19.99/oz
Oribe · Conditioner
Conditioner for Beautiful Color
#50 on the label · $7.65/oz
Oribe · Mask / treatment
Signature Moisture Deep Conditioning Hair Masque
#73 on the label
Oribe · Shampoo
Shampoo for Brilliance & Shine
#76 on the label · $2.35/oz
Identity
What this entry is, and what our references call it.
No public-domain structure depiction is available for this entry.
Citrulline
- citrulline
For your hair?
Whether Citrulline matters for your hair depends on your hair.
10 products in our library list itWhat this ingredient does, and where it sits on the labels we have researched.
A verdict on any product that contains it, and never a safety grade.
We do not physically test your hair. Everything above comes from the ingredient lists in our library and from published references. The consultation is what turns it into a plan.
References
Seed entry, sourcing in progress Written from our reference work; primary sourcing is still being attached.
No published source is attached to this entry yet.
How this page was made
- Every number above is counted from the ingredient lists in our own product library: 10 of 6816 researched products list this ingredient. Nothing on this page is written per ingredient.
- The dots are levels, not scores. Each one comes from what kind of ingredient it is (its chemical class, charge and solubility) or from where it sits on the labels we have.
- US labelling rules put ingredients above 1% in descending order of amount; below 1% they may be listed in any order. Position tells you about relative amount only above that line, and we never convert a position into a percentage.
- The prominence bands (leading, supporting, secondary) are the same ones the product pages use to read a single label, applied here to the median position across a category.
- We do not publish safety scores or hazard grades. Where a regulator has published a restriction or a use condition, we state it and cite it; otherwise we describe what the ingredient does and stop.
- Identifiers and references appear only when a published source is attached to this entry. Without one, we leave the row out rather than fill it in.
- This is cosmetic information, not medical advice, and nothing here diagnoses or treats a health condition.
- Entry last updated 2026-09-22. Product-page methodology: the product library.
