The HGTV designer and her husband and co-star Ben are expecting their second baby girl in May

Erin and Ben Napier were thrilled to discover they were expecting their second child — but the way they found out was far from ideal for the TV stars

"We were filming Home Town Takeover in Wetumpka, [Alabama] and I was suddenly allergic to the facewash I've used for, like, 15 years. My face was on fire, and my skin was peeling," Erin, 35, tells PEOPLE in one of this week's cover stories.

"Which is great the day before you're filming a brand-new show," adds Ben, 37.

"I was incredibly self-conscious and slathering coconut oil all over my face," Erin recalls. "I called one of my best friends, who's an aesthetician, and I was like, "What is the deal?" She was like, "Are you pregnant?" I said no."

ben and erin napier
Credit: Larsen & talbert

Watch the full episode of People Cover Story: Ben and Erin Napier on or on the PeopleTV app.

After a visit to the doctor, they learned that was exactly the case! "It was happy news, and I've been allergic to my favorite face wash ever since," says Erin. "I didn't know that you can suddenly become allergic to things that you've always been fine with. So, watch out everybody, if you're suddenly allergic to something you'd never been allergic to."

"I recently developed an allergy to spicy horseradish. Might be pregnant," Ben jokes.

But Erin quickly shuts him down. "I don't think it's related," she says.

ben and erin napier
Credit: HGTV

Many of the couple's big moments this year happened not in their hometown of Laurel, Mississippi, but about 200 miles away in the small Alabama town where their latest show is set.

In addition to learning they were expecting there, Ben says, "We were in Wetumpka when we found out it was a girl. We've had a lot of milestones in Wetumpka."

The designer and woodworker spent four months traveling back and forth to the town, which had fallen on hard times, and completed 12 major renovations of homes, businesses and public spaces.

WATCH THIS: Erin & Ben Napier Feel "Blessed" to Be Expecting Baby No. 2: "We Didn't Know If It Was Possible"

Erin and Ben Napier family photo
Credit: Brooke Davis-Jefcoat

Baby number two's arrival will thankfully happen closer to home because Ben and Erin are currently shooting season 5 of Home Town in Laurel, and revealing three houses to the homeowners their last week of ilming.

"We're still filming into May. Right when the baby comes, actually," says Erin. "I'm so scared she'll be early. That'll be the danger zone. But it's not going to happen. She's not going to come early."