The claim “I Had No Idea What Apple Cider Vinegar Would Do for My Hair Until I Left It In Overnight” is a common headline on blogs and social media. However, leaving apple cider vinegar (ACV) on your hair or scalp overnight is generally not recommended. While diluted ACV may have some benefits as a short rinse, prolonged exposure can irritate the scalp and damage hair, especially if it is undiluted.
What Is Apple Cider Vinegar?
Apple cider vinegar is made by fermenting apples. It contains:
Acetic acid
Water
Small amounts of vitamins and minerals
Natural compounds called polyphenols
Its acidic nature gives it a pH of about 2–3, making it much more acidic than the scalp and hair.
Potential Benefits of a Diluted ACV Hair Rinse
When properly diluted and used occasionally, ACV may:
1. Help Remove Product Buildup
Hair products, hard-water minerals, and excess oil can accumulate on the hair. A diluted ACV rinse may help remove some residue, leaving hair feeling lighter.
2. Improve Hair Shine
Hair cuticles lie flatter in a slightly acidic environment, which can make hair appear smoother and shinier.
3. Reduce Frizz
Flattening the hair cuticle may also reduce frizz and make hair easier to manage.
4. Support Scalp Cleanliness
ACV has mild antimicrobial properties in laboratory settings, but there is limited evidence that it effectively treats dandruff or scalp infections in real-world use.
5. Balance Scalp pH
Some people find that a diluted rinse helps their scalp feel less oily, although evidence is limited.
What Happens If You Leave ACV on Overnight?
Leaving ACV on overnight can cause problems because of its acidity.
Possible risks include:
Scalp irritation
Redness and itching
Burning or stinging
Dry, brittle hair
Increased hair breakage
Skin irritation around the hairline, ears, or neck
The risk is higher if:
The vinegar is undiluted.
You have eczema, psoriasis, or a sensitive scalp.
Your scalp has cuts or sores.
Your hair has been chemically treated or bleached.
Can ACV Make Hair Grow Faster?
There is no strong scientific evidence that apple cider vinegar stimulates hair growth or prevents hair loss. Healthy hair growth depends on factors such as:
Genetics
Nutrition
Hormones
Overall health
Proper hair care
Does ACV Treat Dandruff?
ACV is not a proven treatment for dandruff. If you have persistent dandruff, medicated shampoos containing ingredients such as zinc pyrithione, selenium sulfide, or ketoconazole have stronger evidence for effectiveness.
How to Use ACV Safely
If you’d like to try it:
1. Mix 1–2 tablespoons (15–30 mL) of apple cider vinegar with 1 cup (240 mL) of water.
2. Shampoo your hair as usual.
3. Pour the diluted mixture over your hair and scalp.
4. Leave it on for 1–5 minutes.
5. Rinse thoroughly with cool or lukewarm water.
6. Use it no more than once a week at first to see how your hair and scalp respond.
Who Should Avoid It?
Avoid using ACV on your hair or scalp if:
You have an irritated, broken, or infected scalp.
You have a known allergy or sensitivity to vinegar.
It causes burning or discomfort when applied.
Your healthcare professional has advised against it because of a skin condition.
The Bottom Line
A diluted apple cider vinegar rinse may help remove buildup and temporarily make hair look smoother and shinier for some people. However, leaving apple cider vinegar on your hair or scalp overnight is not recommended because it can cause irritation and dryness, and there is no good evidence that overnight use provides extra benefits. If you choose to use ACV, dilute it, limit contact time to a few minutes, and rinse it out thoroughly. If you experience persistent scalp irritation, significant dandruff, or hair loss, it’s a good idea to consult a healthcare professional or a dermatologist.