Allergies happen when your immune system overreacts to a normally harmless substance like dust or pollen. Hay fever, hives and anaphylaxis are all types of allergic reactions.

Many of those affected reach quickly for antihistamines to treat mild to moderate allergies (though adrenaline, not antihistamines, should always be used to treat anaphylaxis).

If you’re using oral antihistamines very often, you might have wondered if it’s OK to keep relying on antihistamines to control symptoms of allergies. The good news is there’s no research evidence to suggest regular, long-term use of modern antihistamines is a problem.

But while they’re good at targeting the early symptoms of a mild to moderate allergic reaction (sneezing, for example), oral antihistamines aren’t as effective as steroid nose sprays for managing hay fever. This is because nasal steroid sprays target the underlying inflammation of hay fever, not just the symptoms.

Here are the top six antihistamines myths – busted.

Myth 1. Oral antihistamines are the best way to control hay fever symptoms

Wrong. In fact, the recommended first line medical treatment for most patients with moderate to severe hay fever is intranasal steroids. This might include steroid nose sprays (ask your doctor or pharmacist if you’d like to know more).

Studies have shown intranasal steroids relieve hay fever symptoms better than antihistamine tablets or syrups.

To be effective, nasal steroids need to be used regularly, and importantly, with the correct technique.

In Australia, you can buy intranasal steroids without a doctor’s script at your pharmacy. They work well to relieve a blocked nose and itchy, watery eyes, as well as improve chronic nasal blockage (however, antihistamine tablets or syrups do not improve chronic nasal blockage).

Some newer nose sprays contain both steroids and antihistamines. These can provide more rapid and comprehensive relief from hay fever symptoms than just oral antihistamines or intranasal steroids alone. But patients need to keep using them regularly for between two and four weeks to yield the maximum effect.

For people with seasonal allergic rhinitis (hayfever), it may be best to start using intranasal steroids a few weeks before the pollen season in your regions hits. Taking an antihistamine tablet as well can help.

Antihistamine eye drops work better than oral antihistamines to relieve acutely itchy eyes (allergic conjunctivitis).

Myth 2. My body will ‘get used to’ antihistamines

Some believe this myth so strongly they may switch antihistamines. But there’s no scientific reason to swap antihistamines if the one you’re using is working for you. Studies show antihistamines continue to work even after six months of sustained use.

Myth 3. Long-term antihistamine use is dangerous

There are two main types of antihistamines – first-generation and second-generation.

First-generation antihistamines, such as chlorphenamine or promethazine, are short-acting. Side effects include drowsiness, dry mouth and blurred vision. You shouldn’t drive or operate machinery if you are taking them, or mix them with alcohol or other medications.

Most doctors no longer recommend first-generation antihistamines. The risks outweigh the benefits.

The newer second-generation antihistamines, such as cetirizine, fexofenadine, or loratadine, have been extensively studied in clinical trials. They are generally non-sedating and have very few side effects. Interactions with other medications appear to be uncommon and they don’t interact badly with alcohol. They are longer acting, so can be taken once a day.

Although rare, some side effects (such as photosensitivity or stomach upset) can happen. At higher doses, cetirizine can make some people feel drowsy. However, research conducted over a period of six months showed taking second-generation antihistamines is safe and effective. Talk to your doctor or pharmacist if you’re concerned.

Myth 4. Antihistamines aren’t safe for children or pregnant people

As long as it’s the second-generation antihistamine, it’s fine. You can buy child versions of second-generation antihistamines as syrups for kids under 12.

Though still used, some studies have shown certain first-generation antihistamines can impair childrens’ ability to learn and retain information.

Studies on second-generation antihistamines for children have found them to be safer and better than the first-generation drugs. They may even improve academic performance (perhaps by allowing kids who would otherwise be distracted by their allergy symptoms to focus). There’s no good evidence they stop working in children, even after long-term use.

For all these reasons, doctors say it’s better for children to use second-generation than first-generation antihistimines.

What about using antihistimines while you’re pregnant? One meta analysis of combined study data including over 200,000 women found no increase in fetal abnormalities.

Many doctors recommend the second-generation antihistamines loratadine or cetirizine for pregnant people. They have not been associated with any adverse pregnancy outcomes. Both can be used during breastfeeding, too.

Myth 5. It is unsafe to use higher than the recommended dose of antihistamines

Higher than standard doses of antihistamines can be safely used over extended periods of time for adults, if required.

But speak to your doctor first. These higher doses are generally recommended for a skin condition called chronic urticaria (a kind of chronic hives).

Myth 6. You can use antihistamines instead of adrenaline for anaphylaxis

No. Adrenaline (delivered via an epipen, for example) is always the first choice. Antihistamines don’t work fast enough, nor address all the problems caused by anaphylaxis.

Antihistamines may be used later on to calm any hives and itching, once the very serious and acute phase of anaphylaxis has been resolved.

In general, oral antihistamines are not the best treatment to control hay fever – you’re better off with steroid nose sprays. That said, second-generation oral antihistamines can be used to treat mild to moderate allergy symptoms safely on a regular basis over the long term.

Janet Davies, Respiratory Allergy Stream Co-chair, National Allergy Centre of Excellence; Professor and Head, Allergy Research Group, Queensland University of Technology; Connie Katelaris, Professor of Immunology and Allergy, Western Sydney University, and Joy Lee, Respiratory Allergy Stream member, National Allergy Centre of Excellence; Associate Professor, School of Public Health and Preventive Medicine, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Catherine, Princess of Wales, is undergoing treatment for cancer. In a video thanking followers for their messages of support after her major abdominal surgery, the Princess of Wales explained, “tests after the operation found cancer had been present.”

“My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment,” she said in the two-minute video.

No further details have been released about the Princess of Wales’ treatment.

But many have been asking what preventive chemotherapy is and how effective it can be. Here’s what we know about this type of treatment.

It’s not the same as preventing cancer

To prevent cancer developing, lifestyle changes such as diet, exercise and sun protection are recommended.

Tamoxifen, a hormone therapy drug can be used to reduce the risk of cancer for some patients at high risk of breast cancer.

Aspirin can also be used for those at high risk of bowel and other cancers.

How can chemotherapy be used as preventive therapy?

In terms of treating cancer, prevention refers to giving chemotherapy after the cancer has been removed, to prevent the cancer from returning.

If a cancer is localised (limited to a certain part of the body) with no evidence on scans of it spreading to distant sites, local treatments such as surgery or radiotherapy can remove all of the cancer.

If, however, cancer is first detected after it has spread to distant parts of the body at diagnosis, clinicians use treatments such as chemotherapy (anti-cancer drugs), hormones or immunotherapy, which circulate around the body .

The other use for chemotherapy is to add it before or after surgery or radiotherapy, to prevent the primary cancer coming back. The surgery may have cured the cancer. However, in some cases, undetectable microscopic cells may have spread into the bloodstream to distant sites. This will result in the cancer returning, months or years later.

With some cancers, treatment with chemotherapy, given before or after the local surgery or radiotherapy, can kill those cells and prevent the cancer coming back.

If we can’t see these cells, how do we know that giving additional chemotherapy to prevent recurrence is effective? We’ve learnt this from clinical trials. Researchers have compared patients who had surgery only with those whose surgery was followed by additional (or often called adjuvant) chemotherapy. The additional therapy resulted in patients not relapsing and surviving longer.

How effective is preventive therapy?

The effectiveness of preventive therapy depends on the type of cancer and the type of chemotherapy.

Let’s consider the common example of bowel cancer, which is at high risk of returning after surgery because of its size or spread to local lymph glands. The first chemotherapy tested improved survival by 15%. With more intense chemotherapy, the chance of surviving six years is approaching 80%.

Preventive chemotherapy is usually given for three to six months.

How does chemotherapy work?

Many of the chemotherapy drugs stop cancer cells dividing by disrupting the DNA (genetic material) in the centre of the cells. To improve efficacy, drugs which work at different sites in the cell are given in combinations.

Chemotherapy is not selective for cancer cells. It kills any dividing cells.

But cancers consist of a higher proportion of dividing cells than the normal body cells. A greater proportion of the cancer is killed with each course of chemotherapy.

Normal cells can recover between courses, which are usually given three to four weeks apart.

What are the side effects?

The side effects of chemotherapy are usually reversible and are seen in parts of the body where there is normally a high turnover of cells.

The production of blood cells, for example, is temporarily disrupted. When your white blood cell count is low, there is an increased risk of infection.

Cell death in the lining of the gut leads to mouth ulcers, nausea and vomiting and bowel disturbance.

Certain drugs sometimes given during chemotherapy can attack other organs, such as causing numbness in the hands and feet.

There are also generalised symptoms such as fatigue.

Given that preventive chemotherapy given after surgery starts when there is no evidence of any cancer remaining after local surgery, patients can usually resume normal activities within weeks of completing the courses of chemotherapy.

Ian Olver, Adjunct Professsor, School of Psychology, Faculty of Health and Medical Sciences, University of Adelaide

This article is republished from The Conversation under a Creative Commons license. Read the original article.