I spent major cash on special creams and lotions until a nurse friend clued me in to an astonishingly simple cure.

“Mom, look at this!” My 14-year-old daughter thrust the backs of her hands up to my face to show me that the itchy rash that had been bothering her for weeks had now started to crack and bleed. At first, I thought she just had dry skin from the combination of the cold weather outside and the blasts of dry radiator heat inside. But this was clearly something more than a little seasonal annoyance. My child’s skin—once so soft and perfectly smooth—was now starting to resemble the scales on the amphibian man in The Shape of Water.

Our first attempts at soothing the itch were a disaster: My husband gave her the pricey “all-natural” hand lotion he swears by in the winter, but that just turned her already inflamed hands as red as a boiled lobster claw and had her grimacing with stinging pain.

After that, we headed over to a walk-in clinic, where the nurse-practitioner diagnosed my daughter with eczema, an autoimmune skin disorder that causes inflamed, red, itchy skin all over the body, particularly on the scalp, face, elbows, and hands. She recommended we try Eucerin Crème, which worked, but only a little bit. (At least it didn’t make the condition worse, as the other, irritating moisturizers had.)

Next, I took my daughter to a dermatologist, who prescribed a topic corticosteroid cream. Since I hadn’t reached my deductible on prescriptions yet, that cost me a whopping $129. Again, it helped—but just a little bit.

A few days later, we went out to dinner with our friends Brad and Jaimie, who are both registered nurses. I mentioned my daughter’s eczema, and how nothing seemed to be helping, and Brad turned to me and said, “Forget about all those things. Just use Vaseline. It works, I promise.”

Vaseline? You mean the old jar of petroleum jelly that has been sitting in my medicine chest since my kids were in diapers? Hey, at that point I was willing to try anything.

That night my daughter rubbed the jelly on the back of both hands and went to sleep. The next morning I looked at her hands, and they had literally changed overnight. The rough, red irritated skin on her hands had turned back to its normal color, and though I could still feel the roughness of her skin if I ran my hand over it, she was no longer plagued by itchiness. She continued to rub the Vaseline on her hands a few times a day, and within a week, the eczema seemed to be completely gone from her hands.

I did a little research and found that Vaseline gets a 5 out of 5 rating from the National Eczema Association for containing no known irritants to eczema, and that eczema sufferers have been using it for years.

But best of all, it costs roughly $4 a jar (available on Amazon)—$125 less than the prescription cream that worked half as well!—proving that sometimes the cure your grandmother used is the best of all.