In 2010 the playwright Sarah Ruhl lost her smile. It “walked off my face, and wandered out into the world,” she writes in the opening lines of her new book. Three years earlier, the same thing had happened to me.

We were struck with Bell’s palsy, a type of facial paralysis that occurs when the nerves controlling the muscles on one side of the face are damaged or even destroyed. Why? The science is not conclusive — it could be triggered by a virus, hormones or myriad other factors. The result, though, is devastating. Suddenly you’re unable to convey happiness, sadness and other emotions. There are words you can’t pronounce. Ruhl struggled mightily to say her own daughter’s name — Hope — an irony not lost on her. In her thoughtful and moving memoir “Smile,” Ruhl reminds us that a smile is not just a smile but a vital form of communication, of bonding, of what makes us human.

Bell’s palsy is fairly common, striking about 40,000 people a year in the United States. Among its victims are a few famous faces: Angelina Jolie, George Clooney, Wendy Wasserstein, Allen Ginsberg. In most cases, Bell’s is temporary, lasting roughly three months. For some, though, it can persist and even be permanent. Ruhl and I fall into this latter category.

For me it all began on an ordinary morning, two months before my second daughter’s due date: I awoke to find the right side of my face completely paralyzed. I couldn’t blink or speak clearly. My face was an ugly, unexpressive mess. Although I was only in my 30s, I assumed I’d had a stroke and went to the emergency room, where I was both relieved and concerned to get a diagnosis of Bell’s palsy. I am a professional singer and facial expressions are a part of my livelihood.

Ruhl had a similar experience. Shortly after giving birth to twins, a lactation consultant casually commented “Your eye looks droopy.” When Ruhl looked in the mirror she was shocked by the image that stared back at her: “The left side of my face had fallen down.” She tried to move her brows, eyes, mouth, but could not: “Puppet face, strings cut.” She felt, immediately, as I did, that her identity had changed in an instant. “Before looking in the mirror, I was the same person,” she writes, “After looking in the mirror, entirely different.”

Ruhl, a two-time Pulitzer Prize finalist and recipient of the MacArthur “genius” Fellowship, goes on to chronicle the next 10 years of her journey, or as she puts it, “the story of how I learned to make my way when my body stopped obeying my heart.”

The medical quest involved many approaches that, it must be said, are unavailable to most Bell’s palsy sufferers: acupuncture, chiropractors, therapists, neurologists, options for Botox and surgery (neither of which she utilized) and transformative physical therapy that resulted in a revised smile that, although not like her former one, signified progress and acceptance. Ruhl’s nanny even proved influential beyond child care: Her Buddhist ideals and philosophies proved immensely helpful in Ruhl’s healing. Ruhl may have had access to more resources than most, but her struggles nonetheless feel universal. And that is the thread that binds this beautifully written story.

The chapter “Still Face and the Tony Awards” was particularly compelling — and for me hit very close to home. Ruhl and I both shared the obsession of “not being able to smile fully back” at our babies and the worry that a broken face would impact their emotional growth. After all, the research was clear on the importance of a mother’s face and expression on development. Ruhl describes these concerns with her distinct bluntness: “The effect of the still face on children, the psychologists proved, is, in a word, bad.”

Like me, Ruhl avoided having her photo taken during those early postpartum months. Most mothers who have an album full of early memories take them for granted, but those of us who lose a smile want nothing to do with cameras. As it happens, during this same period Ruhl would be confronting even more photographers: Her play received a prestigious Tony nomination and thus she was compelled to prepare for the infamous red carpet. Photographers pleaded with her to do something she physically could not, one even confronting her: “What’s wrong with you — can’t you smile for your Tony?”

Life with Bell’s palsy, as I can attest, is filled with many moments like those. It feels like an eternity of standing naked in the snow, toggling between literally not wanting to be seen and a desperate desire to be visible in the context of one’s former self (packaged in a slightly different container). Being stripped of one’s face — a symbol of vanity, expression and identity — is a loss almost too painful to describe. Those of us who lose our face often catalogue it like the timeline of Jesus. Both Ruhl and I were raised Catholic, and both of us, although no longer practicing believers, nonetheless prayed to that God when we were struggling with Bell’s. There is a stark “before BP” and “after BP” of our existence, and the shift is palpable.

For Ruhl, balancing a public life, motherhood and the demands of work brought to the fore some fundamental issues of the female experience. Ruhl explores the “complex and unspoken rules” on “whether and how long” a woman smiles and where and when. Every woman who has been asked to smile by a stranger — and that is every woman — will relate to Ruhl’s observations. Imagine dealing with that when you literally can’t smile.

When the months pass and there has been no change to the unrecognizable essence on the front of your head, the anxiety (as if you didn’t already have enough) really begins. The tests. The neurologist’s furrowed brow. But the message is clear: Sorry. Your nerves are completely destroyed. There’s no activity. They may regrow slowly, but they don’t have a path. So in about 18 months you will end up with something called synkinesis. This is where the muscles of your face synergistically and constantly contract, and even bulk up. (I used to call the hypertrophy on my face a mini Arnold Schwarzenegger). For example, when you try to smile, your eye will close. You will look squinty (or as Ruhl calls it, “tiny eye”). They say, “there’s nothing more we can do,” and by that, they also mean, “there is nothing more your insurance will cover.”

Ruhl may have lost the face she once knew but she reminds us that “in truth, we don’t have to win to be grateful. We can always thank the people we love, the people who help us, even when we don’t win an award. We often just forget to.” That’s the kind of simple poignancy that elevates this book.

For this story is also a love story. Throughout, Ruhl’s husband, Tony, is a pillar of strength and empathy. After 10 long years trying to “fix” her face, Ruhl, now 47, has come to terms with it in its improved but still asymmetric state: “I would like to accept my face, my story, as it is written on my face, with joy.” For we are more than our faces, more than our smiles and we are grateful to those who truly see us. Or as Ruhl’s young daughter tells her mother: “I always thought of your face as a beautiful house. A wall suddenly fell down, and you tried to rebuild it, brick by brick. And you couldn’t quite. And all you saw was the wall. But all we saw was the house.”

Heidi Moss Erickson is an opera singer who continues to enjoy a thriving performing career (despite her neurologist’s predictions). She is also a scientist and voice teacher, a professor of vocal anatomy and physiology at the San Francisco Conservatory of Music and a frequent lecturer in the neuroscience of singing.

SMILE: The Story of a Face

By Sarah Ruhl

Simon & Schuster. 241 pp. $27