Dear Doctor: My husband and I are terrible at remembering to wear sunscreen. I don't like how it feels, and he just plain forgets. I recently saw an ad for sunscreen pills. Could they be an option?

Dear Reader: We hate to be the bearers of bad news, but no, sunscreen pills don't work. They have been marketed as dietary supplements that will allow your skin to (magically, it would have to be) ward off sunburn, reduce sun-related aging and even shield you from skin cancer. To paraphrase the Food and Drug Administration, there's no such thing as a sunscreen pill. The risks posed by unprotected sun exposure are serious enough that the FDA put out a statement in May debunking the claims of sunscreen pill manufacturers. It also sent out warning letters demanding that the companies hawking these pills stop their false advertising, which it said violates federal law. The specific companies mentioned in the FDA's announcement are Advanced Skin Brightening Formula, Sunsafe Rx, Solaricare and Sunergetic.

You're right to be concerned that you and your husband have been lax in the sunscreen department. From the instant the sun rises to the moment it sets, amid the spectrum of light that it emits is ultraviolet radiation. The wavelengths of UV rays are shorter than those of visible light, which makes them invisible to the naked eye. But the potential damage they can cause to unprotected skin is considerable.

UV radiation is broken down into UVA, UVB and UVC rays. (We don't hear much about UVC, the shortest of the three, because it gets absorbed by the Earth's ozone layer.) But UVA rays, which are the longest of the three and account for 95 percent of the UV radiation that reaches us on Earth, and UVB rays, which are slightly shorter, do a real number on our skin. UVA, in addition to causing the physiological changes that we call a suntan, penetrates the deepest. It plays a big role in premature aging, and more recent research shows that it plays a part in skin cancers as well. The shorter UVB rays give us sunburns and play a significant role in a range of skin cancers. Both types of UV rays can damage the skin's cellular DNA and thus give rise to genetic mutations that can lead to cancer.

All of this bad news about UV rays would be far more alarming if it weren't for the existence of sunscreens. Legitimate sunscreens are all applied topically. Each contains a mix of certain types of organic and/or inorganic chemicals, which either deflect, reflect, scatter or absorb the UV rays. All types of sunscreens need to be reapplied throughout the day because they either wear off through contact or perspiration, or, if they're absorbing the UV rays, their chemical bonds break down. The array of legitimate sunscreen products is vast.

We think that if you're willing to experiment, you'll find one you don't hate. Just be sure to choose a full-spectrum product that absorbs both UVA and UVB rays and choose an SPF of at least 30. Use sunscreen liberally and reapply often.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My siblings and I are very frustrated that we can't get our grandparents to pay attention to those "excessive heat" warnings that get issued during a heat wave. Can you help? They don't take information coming from us grandkids seriously, but I bet they'd listen to actual doctors.

Dear Reader: You've raised an important -- and timely -- issue and we're happy to help you out. You are right to be concerned because the dangers inherent in hot weather are very real, and the potential consequences can be severe. Between 2015 and 2016, the number of people who died as the result of extreme heat more than doubled from 45 to 94. Just this year, 54 people died during a heat wave in Quebec, many of them over 65.

Here in the United States, excessive heat is generally defined as two or more days in which temperatures exceed 90 degrees, often with correspondingly high humidity. While excessive heat poses a grave health threat to all of us, it is particularly dangerous for the elderly. It's also a threat to the very young, those living in urban centers who are isolated and don't have ready access to air conditioning, and individuals doing physical labor or exercising outdoors. People living with certain diseases, such as cardiovascular and respiratory illnesses, are also at elevated risk.

When we can't stay sufficiently cool, our core temperature will rise. The result is a range of heat-related illnesses. Heat exhaustion is characterized by muscle cramping, headache, fatigue, nausea or vomiting, rapid heart rate, and dizziness or fainting. More serious is heat stroke, in which the core body temperature rises to 103 degrees or more. At this point, the body no longer sweats. Instead, the skin will be hot, red and dry. In addition to the symptoms of heat exhaustion, people with heat stroke will experience confusion and even unconsciousness. These extremes in body temperatures can lead to brain and organ damage. In severe cases, multiple organ failure leads to death.

During an extreme heat warning, you should:

-- Seek out air conditioning. If you have it at home, turn it on. If not, find an air-conditioned public space like a shopping mall, public library, community center or a city-run cooling center.

-- Avoid any strenuous activity.

-- Dress in light and loose clothing.

-- Stay hydrated, preferably with water.

-- If you have any vulnerable family members, friends or neighbors, check in on them.

-- Never ever (EVER) leave people or pets in a parked car for any period of time during an extreme heat event, even in the shade or with the windows open.

With heat waves becoming more frequent and severe, it's wise to plan ahead. Know the locations of public spaces with air conditioning. Use drapes or shades to cover windows. Store plenty of bottled water and drink it. A cool bath or shower can help maintain body temperature. And if someone you know exhibits the symptoms of heat stroke, it's a medical emergency. Call 911, then use whatever means available to cool them down until help arrives.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: How does someone know they're dehydrated? I'm worried because my husband swears he drinks "tons" of water, but as best I can tell, he doesn't have more than a glass or so per day, even when it's really hot. He's very active and he's always got headaches, which he blames on air quality, and he's often tired. How can I persuade him to drink more water?

Dear Reader: Hydration can be a tricky thing. Unlike hunger, which triggers physical signals that are pretty robust, the signs of thirst can be more subtle and easier to ignore. However, drinking enough water is crucial to both physical and mental well-being. The adult human body is made up of 60 percent water. It's the main component of our cells and tissues; it's the environment that makes the various transport systems within our bodies possible, and it plays an essential role in the various chemical and electrical processes that keep us alive and healthy. That means we have to continuously replace the water we lose each day through sweat, urination, breath and in various other physiological processes.

We replenish the water our bodies use through the foods we eat and the fluids we drink. According to the National Academy of Sciences, total water consumption for women should be 91 ounces daily, and for men the number is 125 ounces. Depending on your diet, up to 20 percent of that water will come from foods like fruits, vegetables and liquid dairy products like milk, kefir and yogurt. The balance of the deficit has to be made up through beverages. When it comes to hydration, not all beverages are created equal. Although sodas and fruit juices do provide water, they also deliver a hefty dose of sugar. Coffee, tea and other caffeinated beverages can have a mild diuretic effect. And sports beverages, while marketed to replenish the sodium, potassium and magnesium we lose through sweat, are pretty high in sugar as well.

We can't know for sure the cause of your husband's headaches and fatigue. However, both of those, along with dizziness, loss of appetite, constipation, heat intolerance and blood pressure fluctuations are symptoms of dehydration.

Studies show that we also pay a cognitive price for dehydration. Researchers at the Georgia Institute of Technology found that losing as little as 2 percent of your body weight in fluids -- that's 2 pounds per every 100 pounds that you weigh -- led to impaired decision-making and a lack of mental focus. Not only did motor coordination take a hit when study participants became even mildly dehydrated, they also began to flub mental tasks like reading maps, doing arithmetic in their heads and proofreading. The more dehydrated participants became, the more their performance deteriorated.

In your husband's defense, dehydration can be difficult to discern. It's a somewhat crude measurement, but keeping an eye on urine color can help him to track what's going on. A very dark gold equals dehydration. We hope that learning about the physical and mental toll of skimping on water will persuade your husband to take hydration more seriously.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)