Camilla Jessen
Dry, itchy scalp? Brittle hair that breaks too easily? The problem might not be your shampoo.
Many people go to great lengths for healthier, shinier hair — from salon treatments and expensive serums to heat-free styling routines. But according to hair expert Nicole Petty of Milk + Blush, a common mistake made right in the shower may be doing more damage than we realize: the water is too hot.
“While warm water can help products penetrate better, it can also strip the hair of its natural oils,” says Petty to The Mirror.
The result? Dryness, increased sebum production, dandruff, and brittle strands that are more likely to break. But there’s a simple fix — and it starts with something called the 38-degree rule.
The 38-Degree Rule Explained
According to Petty, hair should never be washed with water hotter than 38°C (100.4°F). That temperature strikes the right balance: it’s warm enough to dissolve dirt and product buildup, but cool enough to protect your hair’s natural moisture barrier.
“Cooler water helps close the hair cuticle, locking in moisture and adding shine,” she explains.
Overly hot water, on the other hand, can cause:
- Scalp dryness and irritation
- Overproduction of oil, making hair greasy faster
- Faded color, especially in dyed hair
- Increased breakage from dehydrated hair shafts
So while steamy showers may feel relaxing, your hair may be paying the price.
How Often Should You Wash Your Hair?
Another common mistake? Washing your hair too frequently.
“How often you should wash depends on your hair type and lifestyle,” says Petty. “But overwashing is a common problem that can damage your scalp and strands.”
Frequent washing can:
- Strip away natural oils that protect and nourish hair
- Lead to dryness, brittleness, and faster color fade
- Cause your scalp to overproduce oil, creating a vicious cycle of greasiness
For most people, two to three washes per week is ideal. If your hair gets oily quickly, it might actually be because you’re washing too often, or using harsh shampoos that disrupt your scalp’s balance.
How to Wash Less Without Feeling Greasy
If you’re used to daily washes, adjusting your routine may take time. Petty suggests:
- Using dry shampoo between washes to absorb excess oil
- Avoiding shampoos with sulfates, parabens, and alcohol, which can irritate the scalp and strip oils
- Gradually increasing the time between washes to allow your scalp to rebalance
Ultimately, it’s not just what you use on your hair that matters — but how and how often you wash it.