Is the 'hygiene hypothesis' a real thing?

Q: Our sister is a messy housekeeper. She calls it the "hygiene hypothesis," and says it's why her kids don't have asthma or allergies and don't catch colds often. Does avoiding antibacterial products and letting the dogs on the couch really keep her kids healthy? We can't tell if she's kidding.

A: We admit that when your letter started out with a mention of housekeeping, we thought you'd written to the wrong columnists. But then you brought it around to an emerging area of study that examines our home environments and their potential effects on health and the immune system. Taken together, these are the basic components of the "hygiene hypothesis," which your sister has been citing.

It's a complex and intriguing collection of theories that began with a specific focus on asthma, but has, over the years, led to a series of broader discussions. In your sister's case, whether or not she's joking, she's referring to questions about our modern-day standards of cleanliness - that is, the ways in which the spaces where we live and work affect our health in general, and our immune systems in particular.

Let's start with the original hygiene hypothesis, which dates back to the late 1980s. It focused on asthma, which is considered to be the most common chronic disease in the developed world. The thinking was that when infants are raised in the ultraclean environments of the modern home, their developing immune systems fail to encounter the wide variety of microbes needed to properly educate their immune systems. This results in immune responses that go awry, leading to an array of childhood allergies and diseases, including the onset of asthma.

Newer related theories suggest being raised in germ-free environments may lead a child's developing immune systems to become trigger-happy. As we continue to learn, an array of so-called "friendly" bacteria, fungi and viruses play a part in keeping our bodies functioning properly. The idea is that reduced exposure to bacteria, fungi and viruses can lead to an overreaction by the immune system when it encounters unfamiliar microbes, including those that don't pose a threat.

It's important to note that so far, these are all just theories. They are subjects of robust debate, and no specific mechanisms for or against these hypotheses have been identified as of yet. Still, as we learn more about the complexities of the human body's connection to the world of microbes, it won't be a surprise if the relationship turns out to be even closer and more complex than we originally suspected.

When it comes to the use of antibacterial household products, we urge caution. Yes, they can be effective at eliminating certain harmful germs. But in the process, they wipe out vast swaths of beneficial microbes and have the potential to play a role in antibiotic resistance. It's not that adherents to the offshoots of the hygiene hypothesis are urging us to live in dirty homes. Rather, it's about striking a reasonable balance between cleanliness and zero tolerance.

Q: Can you please explain about heat exhaustion and heat stroke? We helped out some hikers a few weeks ago who got into trouble in the mountains here on a hot day. We're seeing a lot of inexperienced people on the trails this spring and think this is a useful topic.

A: As the weather warms up and pandemic regulations continue to ease, a lot of people are escaping the confines of home and heading into the great outdoors. Unfortunately, it's easy to underestimate the toll that sun, heat and activity can take on the body. Even on what feels like a mild day, missteps having to do with clothing, terrain, hydration and your level of exertion can turn the sunny weather that drew you outside into a serious health threat.

Heat-related illnesses fall into three categories: heat cramps, heat exhaustion and heat stroke. The mildest of these are heat cramps, although when you're experiencing them, "mild" won't be the first word that comes to mind. They are painful, involuntary muscle contractions that can occur in the calf, thigh, arms or abdomen. Heat cramps are associated with heavy sweating. They can occur during intense physical activity, or in someone exercising beyond their level of conditioning. Someone with heat cramps should move to a shady spot and drink water or a sports drink. Don't resume activity until the cramps have subsided.

The next step on the heat illness continuum is heat exhaustion. Symptoms include heavy sweating, a rapid pulse that may also be weak or irregular, muscle cramps, nausea or vomiting, headache, dizziness, cold or clammy skin, feeling weak and feeling confused. Unless addressed promptly, heat exhaustion can progress to heat stroke, which is a life-threatening emergency. Someone with heat exhaustion should immediately move to a cooler spot and loosen clothing to allow for air circulation. They should use damp cloths to cool the skin, or immerse themselves - including the face and scalp - in cool water. Sip water gradually. Drinking too much may lead to cramps or vomiting.

Someone with heat stroke is at risk of internal injury and even death. Symptoms include hot skin; a rapid, pounding pulse; nausea or dizziness; headache; shallow breathing; confusion or delirium; and a temperature of 103 degrees Fahrenheit or higher. Unlike someone with heat exhaustion, the person with heat stroke will not sweat. Get them to a cool or shady spot and cool their body with water. They urgently need immediate medical care.

We're repeating ourselves, but it's important: Heat illnesses arise from high temperature, humidity, direct sun and physical exertion. The first three heat the body from the outside. Exertion heats you from within.

To avoid heat-related illness, plan ahead. Choose activities appropriate for the day's weather. Wear loose, light clothing, which keeps you cooler than bare skin. Carry plenty of water, and drink it in moderation - you don't want to over-drink. Rest in the heat of the day. Wear a hat and sunglasses. (Some people shade themselves with umbrellas.) Use salty snacks or sports drinks to help replace lost electrolytes. And never ignore the signs of heat illness, in yourself or your companions.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.