It’s the ads, really, that get to Roz.

“It cracks me up to see these ads for TV — for Depends or for glue for your dentures,” says Roz Chast, the great New Yorker cartoonist with the wry style. “The people in them look 55 with a hint of gray. Where are the people who are falling apart? We don’t see that.

“We hear these people say you can live to 120 if you limit your diet to a thousand or 600 calories a day. Do you know anyone who has [quality of life] after 92 or 93? . . . We’re in total denial of that.”

Chast, though, isn’t throwing gallstones at these galling commercial winks to “aging.” She herself was in denial about the more intense realities of elder care till about a decade ago, when her parents’ health began to fail precipitously.

“It’s weird, but I knew nothing about all this,” Chast says by phone from her Connecticut home. “Maybe it’s because my parents and I were complicit in this, but it was an uncomfortable topic for us, and I didn’t have any siblings [to discuss it with]. I didn’t know about house payer proxy forms. I didn’t know if they had a will. I didn’t know about their finances. It was just a lot of stuff that I suddenly had to learn about.”

’Can't We Talk About Something More Pleasant​?’ by cartoonist Roz Chast. (Bloomsbury Publishing)

As her parents began to endure falls and hospital stays and growing anxiety and dementia, Chast — who had made a career of cartooning with a certain neurotic whimsy — began realizing what she was in for. “Friends were going through similar ordeals at the same time, and conversations I had with them were so important and so heartening,” Chast says. “If you haven’t gone through it, you don’t think about it.”

It is this “not thinking about it” part that had become the rule of habit and unspoken ritual for Chast and her long-married parents, and which inspired the title of the cartoonist’s forthcoming memoir, “Can’t We Talk About Something More Pleasant?”

Bob Mankoff, Chast’s editor at the New Yorker, calls the book “an accomplishment — it’s humor from the soul.”

Chast’s reasons for writing it were personal. “I really felt the need to tell this story,” she says. “It sounds really selfish, but this is something I felt so strongly about — that I wanted to write.”

She knew, too, she had so many layers to convey. “There were a lot of aspects to this story,” Chast says, “like my complicated feelings about my parents.” George and Elizabeth Chast called each other their soul mates, even as their daughter lived through profound conflict growing up in their volatile Brooklyn home.

Chast learned to expertly cut that homefront tension with humor. “As Tina Fey writes [in her memoir], it was a way to be the obedient child and still be rebellious and subversive,” she says. “I had to get good grades and do well in school — my mother was an assistant principal and my father was a teacher — and they took this very seriously.

“For me, drawing was an outlet,” Chast continues. “No one in school said, ‘Oh, she can do sports, or she’s pretty,’ but I could draw.”

Now, as an expert storyteller, Chast, 59, is also able to draw out powerful and poignant scenes from her parents’ final years.

“One of the strangest things about that time was my dad” — the same warm and easygoing father who would take her for malteds as a child — “would drive me bananas. . . . I wanted him to stand up to my mother,” Chast says. “She was so overbearing and she would really demean him in public. She was one of those people who was just hot-tempered and very emotional and would just blow up at you, like one of those [cartoon] exploding cigars.”

Toward the end of her father’s life, Chast says she simply realized that her dad “was not a very strong person, and I’m sorry his mother was a nut who was overbearing and cruel to his father. . . . It’s like he was born without a shell.”

“All I felt for him,” she says of her father, “was how much I loved him, and how much he loved me.” George Chast died in 2007. Then the cartoonist hoped for closure with her mother.

“It was more complicated with her,” Chast says. “She loved me, but we never got along — maybe it was a chemical thing, but we could never understand each other.” The artist sought resolution as her mother’s condition worsened, but, as she conveys in the book’s more painful passages, to no avail.

“She liked to say, ‘Oh, trauma time!’ It was as if she had a certain contempt for me.”

Elizabeth Chast — the woman who liked to bellow that her verbal foes would get “a blast from Chast!” — died in 2009. Now, for any closure, the cartoonist would have to write a memoir.

Chast — who began drawing for the New Yorker in 1978 — had published several illustrated books, but this personal a work tapped even greater depths of her talent. Through the hurt, the memoir finds true humor in the specific, like her family home’s “crazy closet,” and the many bankbooks her parents kept for more than a half-century. These passages ripple and resonate with the stuff of deeply lived-in truth.

And when she was done, Chast showed the work to her children, who knew their maternal grandparents well. Her 23-year-old daughter cried sweetly and hugged her, and her 26-year-old son said it was his favorite among her works. The book indeed succeeds at delivering humor from the soul.

“I love my parents,” Chast says. “I did love them. It’s complicated.”