Hello, dear readers, and welcome to our first letters column of the summer. We’ve had a lot of mail -- thank you! -- so we’re diving right in.

-- Let’s start with a question regarding two essential tools of outdoor summer living -- sunscreen and insect repellent. A number of you have written to ask how long these products remain effective. It’s true that most don’t include an expiration date on the packaging. However, the Food and Drug Administration requires sunscreen to maintain its original efficacy for at least three years. (Of course, that means you’ll have to remember when you made your purchase.) Most manufacturers say their insect repellents remain effective for two to three years. If you need a more precise answer, you can call or email the manufacturer’s customer service department and provide them with the lot number of the product you’re asking about.

-- A column about the unhealthful nature of processed foods puzzled a reader from Iowa. “Can breakfast cereal, which is extruded, molded and milled, be considered a healthy processed food?” she asked. The answer is that it depends on the specific cereal. Those that are made from whole grains, have little-to-no added sugar and salt, and are high in fiber can be considered healthy-ish. (Emphasis on the “ish.”) Eat them with a serving of fresh fruit, watch portion size and don’t dip into the sugar bowl. Cereals fortified with vitamins, minerals and iron can contribute to daily nutritional goals.

-- A reader in Virginia thought we left out an important detail in our discussion of preventing deep vein thrombosis, which is the formation of blood clots, on long plane flights. “Never once did you mention wearing compression socks on the flight,” he wrote. “Doesn’t that help prevent DVT?” You’re correct that wearing compression socks or stockings can help reduce the risk of developing deep vein thrombosis. According to the National Institutes of Health, about 2 out of every 10,000 passengers develops DVT on a long flight. For those at high risk, knee-high compression stockings with compression strength between 15 and 30 mmHg are a good idea.

-- We received a lot of mail in response to a column about the importance of vitamin B12, an essential vitamin the body needs but doesn’t produce. The answers to your varied questions are: B12 is manufactured by bacteria living in the guts of a variety of mammals, fish and poultry. It’s available in animal products, including fish, meat, poultry, eggs, milk and milk products. It’s also available as a supplement, both over-the-counter and through prescription. OTC products, although not regulated by the FDA, are considered to be a reliable source of the vitamin. Studies have found no advantage of sublingual (under the tongue) B12 over tablet form. Most B12 supplements exceed the recommended dietary allowances (RDA) for adults of about 2 to 3 micrograms per day. However, the body absorbs only as much as it needs, and any excess of the water-soluble vitamin is excreted in the urine.

Thank you to everyone who wrote with kind words. We’re thrilled that you continue to find this column both interesting and useful. We look forward to seeing you again in this forum next month.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I got bitten by a tick, and my doctor said it might make me allergic to meat. That was a few months ago, and I can still eat a hamburger and not get sick. How long does it take for the allergy to start? Will it ever go away?

Dear Reader: It sounds as though you were bitten by Amblyomma americanum, commonly known as the Lone Star tick. Adults are reddish-brown in color, with a rounded body. Females have a single white splotch at the center of their backs, the distinctive “star” that gives the arachnid (that’s right, ticks are not insects) its name. Males have white markings around the edge of their bodies, sometimes in the shape of a horseshoe, but these are often not as noticeable.

Entomologists say the Lone Star is an aggressive tick that actively seeks out its prey. It’s abundant throughout the southeastern United States, and is found along the Eastern Seaboard. As is happening with many species of tick in the U.S., the Lone Star tick has been steadily moving north and west, gradually expanding its range.

As your doctor explained, a growing body of evidence suggests that this species of tick can cause those who have been bitten to develop an allergy to red meat. Specifically, the tick bite causes the immune system to become sensitized to a sugar molecule found in most mammals, but not in humans. Known as galactose-a-1,3-galactose, it’s commonly referred to as alpha-gal. Symptoms of alpha-gal syndrome include hives, rash, nausea, stomach pain that can become severe, difficulty breathing, dizziness, and swelling of the lips, mouth or throat. In rare cases, a severe and potentially fatal allergic reaction known as anaphylaxis is possible.

Unlike in other food allergies, such as to nuts or eggs or shellfish, which trigger a reaction within minutes of consumption, the symptoms of alpha-gal syndrome typically take anywhere from three to six hours to appear. Researchers suspect this is because the allergy is to a sugar molecule rather than to a protein. Also, it appears likely that the meat must be digested in order to release the alpha-gal molecules. This delay can make connecting the symptoms to their cause a challenge.

Not everyone who gets bitten by the Lone Star tick will go on to develop a meat allergy. The syndrome is so new that the interval between the tick bite and the onset of a meat allergy remains unclear. However, data suggests it can range from two weeks to several months. You can get a definitive answer regarding your status by having a simple blood test, which looks for the presence of IgE antibodies, which are specific to alpha-gal. As for how long the allergy lasts, again, no one knows for sure. There is evidence that, barring subsequent Lone Star tick bites, which would reactivate the immune system, the meat allergy can fade over time. Alpha-gal is not normally found in fish or birds, which means anyone who develops the syndrome can safely eat fish and poultry.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Our older sister has become a hoarder. The halls in her house are filling up with junk, and you can’t even get into her kitchen anymore. My brother and I worry she’s not safe. Why does a hoarding disorder happen? How do we help her?

Dear Reader: Hoarding disorder is a recognized diagnosis in the DSM-5 -- the Diagnostic and Statistical Manual of Mental Disorders, which is the authoritative guide to the diagnosis of mental disorders. People who are hoarders struggle to discard or part with possessions that others see as useless. They acquire and store vast amounts of stuff, which compromises the function and safety of their homes. When asked why, they will express the belief that the objects have either monetary or sentimental value, or that they may be useful in the future. While other people see accumulations of old newspapers, magazines, plastic bags, tools, broken furniture or household items as worthless junk, these things exert a powerful mental and emotional pull on the person who amassed them.

You and your brother are correct that a hoarding disorder can pose a real risk to health and safety. There’s the danger of trips or falls. The inability to use a bathroom, bedroom or kitchen as intended interferes with both physical well-being and hygiene. Piles of stuff often block ventilation or heating ducts and obstruct windows and doors, which create safety and fire hazards. Cramped and chaotic conditions encourage dust, mold or mildew, as well as insect and rodent infestations. All of this can lead to structural damage to the home, and even pose a danger to neighbors.

There are psychological harms as well. People who hoard often live with a profound sense of shame. And as you are experiencing, hoarding affects the family as well. It can cause relationships to become strained or impaired, and for many people who hoard, the disorder leads to social isolation.

It’s important to understand that hoarding has nothing to do with being messy, lazy or indecisive. Instead, it’s a mental health disorder. People who hoard struggle to decide when to throw something away. When faced with discarding or giving away their possessions, they experience great distress and anxiety. Researchers have linked hoarding to obsessive-compulsive disorder, or OCD, and to depression and anxiety disorders. Scans of hoarders asked to divide mail into ”keep” and “discard” piles have shown spikes of activity in the emotional centers of the brain.

When it comes to helping someone with a hoarding disorder, persuasion, logic or arguments don’t work. Neither does force. Instead, experts recommend beginning by clearly stating your concerns for the person’s health and safety. Most hoarders know that something is wrong, and that their living situations are both peculiar and dangerous. Then, provide avenues of assistance. Some people find help with cognitive behavioral therapy, in which the individual is guided to identify and understand their thinking patterns, and then focus on gradual change. Individual therapy with a specialist in hoarding disorders can be helpful, as can group therapy, which allows the person to see they are not alone. You can find more information and resources at the Anxiety and Depression Association of America’s website, at adaa.org.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)