If you’ve smugly enjoyed the dystopian worlds of “The Handmaid’s Tale” (where infertility is triggered in part by environmental pollutants) or “Children of Men” (where humanity is on the precipice of extinction) — and believed that these stories were rooted firmly in fantasy — Shanna Swan’s “Count Down” will serve as an awakening.

“Count Down,” which Swan wrote with the health and science journalist Stacey Colino, chronicles rising human infertility and warns of dire consequences for our species if this trend doesn’t slow. The reason, Swan explains, may be growing exposure to “endocrine disrupting chemicals” that are found in everything from plastics, flame retardants, electronics, food packaging and pesticides to personal care products and cosmetics.

She outlines the danger. These substances interfere with normal hormonal function, including testosterone and estrogen. Even in small doses, they pose particular danger to unborn babies and young children whose bodies are growing rapidly. These hormone-warping chemicals, which can enter even the placenta, have the ability to alter the anatomical development of girls and boys, change brain function and impair the immune system.

Swan is a noted environmental and reproductive epidemiologist who has studied this subject for more than two decades. Her work on falling sperm counts garnered worldwide attention in 2017. Media coverage focused on her central finding: From 1973 to 2011, the total sperm count of men in Western countries dropped by 59 percent. The quality also nose-dived, with more odd-shaped sperm and fewer strong swimmers capable of fertilizing an egg. Perhaps most important, the DNA they carried was also more damaged.

A study Swan cites in “Count Down” found that just over a quarter of men experiencing erectile dysfunction were under 40. That may be, in part, because testosterone levels have been dropping at 1 percent per year since 1982. The outlook for women isn’t good either. The miscarriage rate has risen by 1 percent per year over the last two decades. If these trajectories continue, in vitro fertilization and other artificial reproductive technologies may become a widely needed tool for conceiving children.

Swan distills information harvested from hundreds of published studies and while some ring familiar, the conclusion she reaches hits hard. These chemicals are limiting the ability of current and future generations to have children. They could, ultimately, snuff out the human species altogether.

This is why Swan was compelled to write this book, one with apocalyptic implications. Despite the publicity, these alarming findings haven’t sparked changes in environmental policies, regulations or public demand for safe substitutes.

Her focus on male infertility marks an overdue inflection point, with the medical community’s acceptance that the health of both sexes is equally important. When a couple can’t conceive or a woman miscarries, she usually bears the blame. Swan dispels the myths surrounding reproductive failure. Yes, as women get older, their ability to get pregnant drops, but Swan reminds us that a man’s reproductive clock is also ticking as he ages. Abnormal sperm, increasingly common in men over 40, can also cause miscarriages.

Teasing out the mechanisms behind plummeting fertility rates is complicated. While man-made chemicals certainly play a role, Swan emphasizes that timing matters, with different impacts for those exposed in utero, as newborns, adolescents or adults. She walks the reader through the reproductive problems that result from contact with flame retardants, pesticides and what she calls “an alphabet soup” of chemicals.

For men, phthalates, found in many products, from plastics to shampoos, are the worst offenders, tanking testosterone levels and sperm counts — and causing sperm to basically commit suicide. In women, these chemicals may cause early menopause or cysts in the ovaries, or they may disrupt monthly cycles.

Bisphenol A, a ubiquitous chemical used in hard plastics, electronics and millions of other items, affects both sexes but is particularly concerning for women. It interferes with conception and causes miscarriages early in pregnancy.

Swan broadens her argument by documenting how these chemicals are jeopardizing the survival of many other creatures. Genital abnormalities are of great concern: distinctly smaller penises in alligators, panthers and mink, as well as fish, frogs, snapping turtles and birds that appear to have both male and female gonads, and mating difficulties in many species caused by altered behavior.

Swan highlights another layer of risk. Parents’ exposure to these chemicals can affect the sexual development of their children. If a woman smokes when she is pregnant, her son’s sperm counts may drop by 40 percent — and if he is later exposed to endocrine disruptors, his sperm production may drop so low that he becomes infertile. Swan describes the collateral damage caused by a combination of lifestyle factors — such as stress or bad diet — and daily exposure to toxic chemicals. The effects can radiate down through several generations.

Although most of Swan’s analyses focus on Western countries, she has uncovered similar trends in South America, Asia and Africa.

Swan offers a sense of relief in her wrap-up, providing practical advice on steps that individuals can take to protect their health. She goes beyond lifestyle recommendations, outlining a far more difficult task: Purging harmful chemicals from our homes by reading the ingredients on bathroom and kitchen cleaners. Choosing personal care products that are phthalate-free and paraben-free. Ditching air freshener and scented products. Not microwaving food in plastic, making sure to filter drinking water and toss out plastic food storage containers and nonstick cookware. The suggestions go on.

Swan does miss an opportunity to give more attention to real-life stories. When she mentions individuals, their reproductive problems are often described without the history or context that strengthens a narrative. There are times when a memorable personal story might have supplanted a rather detailed anatomical and chemical description. There are passages that suffer from what Swan herself refers to as “stat overload” or dozens of foreign-sounding chemical names.

Over all, her conclusion is well supported: the need for regulation, specifically United States federal policies that require companies to prove chemicals safe before using them commercially. Europeans favor this precautionary principle and are currently phasing out or banning the most dangerous chemicals. Swan underscores how this contrasts with the American approach of “innocent until proven guilty,” which then requires taxpayer-funded government studies to investigate health effects.

“Count Down” is an important book for anyone concerned about the environment, pollution, successful childbearing or declining health of the human species. Other than the pervasive chemical names, it is written in a casual, accessible style and will be of practical relevance to couples and young adults who are considering having a family.

Fertility is already an issue for some who have children later in life, when the effects of these chemicals may be more pronounced. Swan offers somewhat bracing recommendations for women who choose to delay pregnancy: Freeze your eggs in your 20s as an insurance policy. For men, investigating their sperm count early might reveal infertility trends when they are easier to correct. More broadly, this book provides a wake-up call that increases understanding of fertility, its challenges and the recognition that both partners play a role.

But ultimately her conclusion is a plea for swift national and global actions that ban the use of these chemicals and mitigate the effects of those that are impacting health and even life itself worldwide. Swan makes it clear that the future of many species, including our own, depends on it.