I’m a doctor — here are 3 easy ways to get your hair from haggard to healthy

Your old hair care routine isn’t cuttin’ it.

Dr. Charles Puza, a Harvard-educated, board-certified dermatologist based in NYC, is revealing his holy trinity for healthy hair.

In a TikTok last month, he recommended changing up shampoos, blow-drying hair on the cold setting and utilizing hair masks.

1. Stop using the same shampoo every day

As Puza explained, just as your skin care needs change, so does your hair care.

He recommended rotating products to suit the needs of your scalp, a process called hair cycling.

For example, a ketoconazole shampoo can combat Malassezia fungus, a major cause of dandruff. For its part, a selenium and salicylic acid shampoo can decrease visible and invisible dandruff.

As Puza insisted, “Even background dandruff is bad for your hair.”

Hair cycling is also endorsed by Healthline Media’s clinical adviser, Dr. Meredith Goodwin.

She told The Post earlier this year, “Because each shampoo/conditioner combination ends up leaving a different coating (or no coating) on the hair shaft that often builds up after consistent use, many people note that changing that shampoo/conditioner combination improves the feel of their hair.”

2. Don’t let your hair air-dry

Puza explained that air-drying is also a no-no. “Stop air-drying your hair, and don’t let it stay wet for too long,” he advised.

He insisted that a blow-dryer on cold is the healthiest way to dry damp hair.

Brushing wet hair is also frowned upon in hair care, as it can damage strands.

Bronwen Robinson, a senior hair stylist and educator at Suite Caroline in Soho, recently told The Post that wet hair is akin to “wet spaghetti,” meaning that it can easily stretch and break. She recommended getting the knots out with a natural fiber brush — never hard plastic — before getting it wet.

3. Use leave-in conditioner

Just as skin can benefit from a peel and exfoliation, hair can also be improved with concentrated TLC.

Puza supported a weekly ritual of leave-in conditioner: “These hair masks are a game-changer.”

The Post recommends Living Proof No Frizz Leave-In Conditioner as a well-rounded cure-all.

And Chris Appleton + Color Wow Money Masque is one of The Post’s favorite hair masks.