Dear Doctor: Our 68-year-old father moved to Hilo on the Big Island of Hawaii two years ago. He's not that great about using sunscreen, so my siblings and I always figured skin cancer would be the biggest health threat. But now with the Kilauea volcano, we're way more worried about the toxic fumes. What are they, and are they really as dangerous as the news stories say?

Dear Reader: When your father relocated to the Big Island, he moved to the youngest of the chain of Hawaiian Islands. It's home to Kilauea, which, despite its outwardly quiet demeanor over recent decades, is considered to be one of the most active volcanoes in the world. In fact, according to the U.S. Geological Survey, Kilauea has been in the process of erupting since 1983. This occurs when magma, the mixture of molten or semimolten rock found beneath the earth's crust, makes its way to the surface.

As this happens, ash, steam and various gases dissolved in the magma are released. Among the emissions is sulfur dioxide, or SO2. It's a noxious gas that in certain concentrations is toxic and potentially deadly. Scientists monitoring the current stage of Kilauea's eruption, which as we've seen from news reports is extremely active, report that significant amounts of the gas are emerging from the volcano's various vents and fissures.

Sulfur dioxide is a colorless, nonflammable gas with the acrid odor of a just-struck match. It's a byproduct of the burning of coal and oil at power plants, of smelting copper and, as Kilauea now reminds us, of volcanic eruptions. In small quantities, SO2 is used as a food preservative, as in dried fruit. It's also used to sanitize food containers and fermentation equipment, and as a moisture control agent.

People exposed to the gas near the volcano may experience eye irritation that can become severe, sneezing, coughing and choking, and a burning sensation or even a rash on the skin. Prolonged exposure to SO2 can cause bronchitis and swelling of the upper airways to the point that breathing becomes difficult or impossible. That's because the gas is highly soluble in water and is easily absorbed by the moist environment of the respiratory tract. SO2 gas is bad news for anyone, but the young, elderly and those with breathing issues are at greater risk of serious side effects. This is why residents have been evacuated from the immediate area and have been allowed to return to fetch pets and valuables only when it has been determined that SO2 is at acceptable levels.

Living in Hilo, a safe distance away from the volcanic activity, your father isn't at direct risk from SO2 gas. However, falling ash, as well as a mixture of SO2 and water vapor from fog or rain, known as "vog," can affect air quality across a wide radius. If your dad has any breathing issues, it's possible that they may flare up as the present eruption continues to affect air quality in a wider area. Staying indoors and avoiding exertion can help protect him from the worst of it.

(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: I have heard recently from a friend that watching internet pornography can lead to erectile dysfunction. Is this true?

Dear Reader: Your friend may not be far from the truth. To put it simply, the rates of erectile dysfunction have significantly increased over the last 15 years. This has especially been noted in men younger than 40. In 2002, a review of 23 studies from Europe, the United States, Asia and Australia found that the rate of erectile dysfunction in that age group was 2 percent. But in 2011, a study of Europeans found that the rate of erectile dysfunction in men ages 18 to 40 ranged from 14-28 percent. Further, a 2014 study of 367 military personnel ages 21 to 40 found erectile dysfunction in 33.2 percent of the men. Even when excluding military personnel with post-traumatic stress disorder, the rate of erectile dysfunction was 15.7 percent.

Older men can have many physiologic causes for erectile dysfunction, but these are much rarer in younger men. Among such causes are vascular disease from years of smoking, high blood pressure and diabetes. Further, while rates of obesity and diabetes have increased among those under 40, the rate of cigarette smoking has decreased. So, if the risk factors for ED have not increased substantially, why the dramatic risk in ED? Some have said that the increase in erectile dysfunction has coincided with easy access to internet pornography.

In fact, many studies have found a correlation between an increase in pornography use and a decline in sexual desire, sexual arousal, enjoyment of sexual intimacy and sexual satisfaction as well as more sexual problems, such as erectile dysfunction. Addiction to pornography seems to affect the brain reward pathways, leading to a reward mechanism that can only be fulfilled with cues found in pornography and dulling the brain's responsiveness to normal sexual stimuli. In a way, increasing pornography desensitizes the individual to sexual stimuli.

However, two studies contradict the idea that internet pornography leads to greater erectile dysfunction. The first -- a study of 280 men -- found a correlation between a weekly increase in the watching of sexual stimuli and a mild increase in the desire for sex. The second -- an online European study of 2,737 men under the age of 40 -- found no link between the use of pornography and sexual dysfunction, though it did find higher rates of low sexual desire than had been reported in past studies of this age group.

Ultimately, pornography may not be the underlying issue. For one, more men may be using pornography because of a greater feeling of isolation and a greater inability to be sexually intimate. Second, a society that spends much of its time on computers, both in work and personal time, fosters a decrease in -- and alteration of -- human contact, which may lead to anxiety with sexual intimacy.

The fact remains that the rates of erectile dysfunction are increasing in men younger than 40, and while pornography may be part of the equation, it may actually be a symptom and not a cause. The bigger issue may be greater social isolation and difficulties with intimacy.

(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: Just how unsafe is chromium-6, the chemical at the heart of the movie "Erin Brockovich"? I read that it's still in the water in some parts of the country. How is that possible? How do I find out about water quality in my area?

Dear Reader: While the characters and events in "Erin Brockovich" may have been embellished to serve the dramatic arc of the story, chromium-6, when present beyond certain concentrations, is as toxic as the film portrayed. Breathed in, it can cause lung cancer. Ingested, it has been linked to liver and kidney damage, serious reproductive problems, rashes and skin conditions, and developmental harm to infants and children.

Chromium is a metallic element that occurs naturally in soil, rocks, plants and volcanic dust. It is found in several forms, including chromium-3, an essential micronutrient that plays a role in the breakdown of fats, proteins and carbohydrates. Chromium-6, by contrast, is a toxic form of the element. Also known as hexavalent chromium, it's a byproduct of the natural chemical breakdown of chromium and is created in greater quantities through various industrial processes.

Both forms of chromium are used in applications such as chrome plating, making pigments and dyes, the manufacture of stainless steel, preserving wood and leather products, and, as depicted in "Erin Brockovich," in the treatment of water in cooling towers. Exposure to large amounts of any kind of chromium, which has numerous uses in manufacturing, has been known to cause respiratory problems like shortness of breath, wheezing, cough and even asthma.

When industrial users of chromium-6 fail to take proper precautions when they store or dispose of the chemical, leakage and runoff from the manufacturing process can pollute the groundwater. And while the EPA has set a limit on what it refers to as "total chromium," the sum of chromium-3 and the far more toxic chromium-6, at this time it has not set a limit solely for chromium-6. California, home to the landmark chromium-6 lawsuit at the heart of "Erin Brockovich," has placed a legal limit on chromium-6 concentrations in the water, but some activists believe the allowable levels remain too high.

You've posed an important question when you ask about how chromium-6 continues to enter our drinking water supply. But the answer is complex. Providing potable drinking water to a nation as vast and populous as the United States remains an ongoing challenge. Since the establishment of the Clean Water Act in 1972, health and safety standards have been set at the federal level. However, water is a regional resource. That means oversight of the tens of thousands of state, local and private water utilities that make sure our taps are flowing falls to a complex patchwork of regulatory agencies. As a result, water quality can vary greatly depending on where you live.

If you live in a community whose water system serves more than 100,000 people, it is required to post reports on water quality online. If you live in a smaller community, check with your local government agency to learn where and how to find reports regarding your specific provider. For more information, go to water.epa.gov/drink/index.cfm.

(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.)