If ever you’ve had the urge to perform a random act of kindness, think about aiming it in the direction of a caregiver — and what better time than the holidays.

Imagine what it might be like to wind up doing a job you never trained for, were totally unprepared for, and never really wanted to do. It’s a job that can require you to be at work 24 hours a day, seven days a week, with no holidays, no lunch break and no chance for promotion. Oh … and it pays nothing. You might be thinking parenthood, but this is something different. Something equally, or more, demanding.

You never really applied for this job — but you were hired, as so many people are, with a phone call telling you your mother had a stroke, or your spouse was injured on active duty. On that call, you heard your mother or spouse needed someone to lend a hand to help navigate life’s necessities — what the jargon-lovers call “activities of daily living” — such as getting dressed, staying nourished and tending to hygiene.

Overwhelmingly, people don’t think twice and say “yes, of course.” They are loving, generous sons and daughters, partners, wives and husbands, or even close friends, just doing what families and friends do. That’s the way they see themselves, but they are, in fact, caregivers. Some come to the role more gradually, beginning with a little help grocery shopping or driving a neighbor to doctors’ appointments. Maybe they live at a distance and volunteer to pitch in with bill-paying or taking care of insurance claims. As needs change, and if health deteriorates, the job can become increasingly demanding. Full time. Round the clock.

Close to 40 million people in the United States provide unpaid care to an ill or disabled adult, often single-handedly. Only half of them say they get any unpaid assistance from other family or friends. Sixty percent of caregivers are also holding down a paying job, and more than two-thirds of them use their own money to provide care. Those age 75 and over are typically the sole support of their loved ones. Nearly a quarter of America’s caregivers are millennials, between age 18 and 34, and they’re equally likely to be male or female.

The value of this unpaid service? About $470 billion a year. That’s more than the entire Medicaid budget in 2013. That’s equal to Wal-Mart’s annual sales. Family caregiving is, in fact, the backbone of what passes for a long-term care system in the United States.

Caregiving can be an exhausting, lonely job — and it can be joyful and rewarding. Most of it is done in a spirit of great gratitude and love. A recent photo essay in AARP The Magazine features eight caregivers assisting adult children, brothers and sisters, parents, friends and neighbors who are ill or disabled. They include a 75-year-old helping her 57-year-old friend with COPD; a wife caring for her husband who was wounded by a mortar attack in Iraq, and a son helping his mother who is disabled with rheumatoid arthritis.

Other examples abound: traumatic brain injury, cancer, Alzheimer’s, Parkinson’s, Lou Gehrig’s disease (ALS) and post-traumatic stress disorder (PTSD). Overwhelmingly, people want to maintain as much independence as possible and remain in their homes and communities as long as they are able. And most are adamant about not wanting to be a burden to friends or family. Caregivers make that possible.

Yet caring for a loved one has grown harder and more complicated. Families have more demands on their time, each of us is living longer, and hospitals are releasing patients earlier. Veterans are coming home more profoundly affected.

Caregivers can find themselves performing medical tasks that would make student nurses quake. Complex wound care, administering IVs, and sorting out multiple medications are often part of the routine, along with bathing, toileting and physical therapy. They also navigate the health care system, provide emotional support, arrange rehabilitation, and handle the family’s legal and financial matters — and they might well be raising their own children at the same time.

As unstinting as caregivers are with their own time, they often feel emotionally and physically overwhelmed. That’s where each of us can help a little.

Small acts of kindness can have a big impact. They don’t have to be anything complicated or expensive. You can shovel snow from a driveway or sidewalk, arrange a play date for their kids, offer the gift of time away, make a meal or grab their grocery list. If it’s someone who is taking care of a veteran, you might suggest that they contact the Elizabeth Dole Foundation, which is dedicated to supporting military families and caregivers. Making specific offers tends to work better than asking a caregiver “to let you know how I can help.”

You might want to ask your friends and colleagues about their caregiving experiences. Chances are, you will find almost everyone has a caregiving story. Chances are, if you’re not already a caregiver, you will become one or need one at some point in your life.

I have been a caregiver, and I can assure you: A random act of kindness is an enormous gift, any time.

Jo Ann Jenkins is CEO of AARP.