Friday April 13 2012
Lack of evidence for insect bite treatments does not mean they are ineffective
Over-the-counter insect bite remedies are not worth buying, the Daily Mail has reported. The newspaper said a review of the evidence on treating insect bites has found that there is little research to prove they are effective.
To conduct the new review, experts looked at the general evidence on various treatments for insect bites not accompanied by complications, such as infections or serious allergic reactions. Treatments examined included simple painkillers, antihistamines and steroid creams. For most treatments, the researchers said there was a lack of direct evidence that they work for treating insect bites.
The new review of the evidence is useful, but did not involve an exhaustive search for studies. Therefore, it may not have included the best research on this topic. Also, despite the lack of research specifically on insect bites, some treatments such as simple painkillers and local corticosteroid creams are considered helpful by experts for mild reactions, such as inflammation and swelling in general. Allergic skin reactions can be treated with antihistamine tablets or capsules.
Occasionally, an insect bite can lead to complications which may need treatment, including infection and eczema. In a small number of cases, an insect bite can result in a dangerous reaction called anaphylactic shock. In this case, medical help should be sought immediately. There are also effective means for preventing insect bites, which are particularly important in countries with a risk of malaria.
It’s also worth remembering that a lack of evidence for a particular treatment is not the same as evidence that it is not effective.
Where did the story come from?
The study was carried out by authors from the Drugs and Therapeutics Bulletin, a journal for doctors, pharmacists and other healthcare professionals. It was also published by this journal. There was no external funding.
It was widely covered in the papers, which generally concentrated on the lack of evidence for over-the-counter remedies.
What kind of research was this?
This was a general review of the evidence on the management of simple bites by insects commonly encountered in the UK, such as midges, mosquitoes, biting flies, fleas and bedbugs. It pointed out that although insect bites are thought to be common, the actual incidence is unknown. An insect’s saliva, once injected into its victim, contains a number of substances which can cause a variety of responses. These range from mild local reactions to allergic reactions (such as anaphylactic shock) and infections. The review only covered simple insect bites and not those that are followed by anaphylaxis or a systemic infection.
This was not a systematic review of the evidence for the management of insect bites, so it is not certain that its authors included all the best research on the subject. A systematic review would have included a comprehensive search of several databases for relevant study data on the topic and would have described the strict criteria used to assess the quality of research found.
What were the basic results?
The authors said that there is a lack of evidence on whether many available treatments work. They also said that, in general, recommendations for treatment are based on expert opinion and clinical experience rather than study data. Their paper reviewed what evidence there is for the management of simple bites by insects commonly encountered in the UK, but excluded ticks, mites and lice. Below are the review’s main findings of different treatments for simple insect bites.
Oral antihistamines (tablets and capsules)
Antihistamines are widely recommended by experts to treat itching associated with insect bites, although apparently few studies support their use. Guidelines recommend the use of non-drowsy antihistamines during the day and sedating antihistamines at night, if sleep is interrupted. Topical antihistamine creams applied directly to the skin are generally not recommended.
Corticosteroids (creams and tablets)
Corticosteroid creams are recommended in doctors’ guidelines, although the researchers say no studies have been found to support their use for insect bites. They suggest they should be used sparingly and for a short time to reduce the risk of unwanted effects. Topical hydrocortisone cream is available over-the-counter and is commonly recommended to reduce inflammation and itching, but should not be used on the face or on broken skin. Corticosteroid tablets are recommended in guidelines for more severe reactions, but again there is no published evidence to support their use and they can cause adverse effects.
Painkillers and local anaesthetics
Simple painkillers such as paracetamol and ibuprofen are recommended by experts for painful insect bites. However, once again the researchers say no published evidence was found to support this use. Topical anaesthetics such as lidocaine are included in some over-the-counter products for insect bites, but are thought to be only marginally effective.
Crotamiton lotion or cream is recommended by experts, but the researchers say they have found no evidence to support its use. Calamine lotion is not recommended.
One small trial of dilute ammonium solution found it relieved symptoms such as itching and burning compared to a placebo.
Other medicines and lotions
Other over-the-counter and prescription products sometimes recommended for insect bites include antiseptics (such as chlorhexidine) and astringents (such as aluminium sulphate). The researchers say there is also a lack of evidence supporting their effectiveness. Some topical preparations can cause allergic and sensitivity reactions, which can exacerbate the original symptoms of a bite.
Managing complications of insect bites
The guidelines above apply to insect bites without complications, but the researchers also point out the importance of treating insect bites with complications, such as infections:
- If an insect bite causes general symptoms of allergy or if there is a large area of redness and swelling, patients should be referred to an allergy clinic.
- If there is a bacterial infection, guidelines recommend treatment with antibiotics.
- Severe reactions such as anaphylaxis should be treated urgently. Adrenaline should be administered as soon as possible and the patient admitted to hospital.
How did the researchers interpret the results?
The authors say there is little direct evidence for the effectiveness of treatments for simple insect bites and that guidelines on their management are generally based on expert opinion. In many cases, no treatment may be needed and, for mild local reactions, a cold compress often suffices.
This review provides a useful round-up of the current approaches for treating simple insect bites. These approaches, the authors say, are generally based on expert opinion and clinical experience, rather than evidence from studies. However, as this was not a systematic review, it did not necessarily include the best research on the treatments it discussed, and there may be valid studies supporting the use of these treatments which the authors have not encountered. It is also worth remembering that, even if there is no direct evidence supporting a particular treatment, this does not mean it is not effective. Rather, it indicates that we can’t be certain whether a treatment is effective.
The review’s focus on the lack of research evidence for particular remedies is useful. However, some treatments, such as painkillers and antihistamines, are known from clinical experience and broader research to generally reduce pain and allergic reactions.
There are also effective pharmaceutical options, such as insecticides, for preventing insect bites. These can be important when going abroad, particularly to ward off malaria-carrying mosquitoes. Anti-malarials are also important for reducing the risk of infections if mosquitoes do bite. Even in the UK, insect bites can cause potentially serious complications such as bacterial infections, and there is clear evidence that antibiotics can stop these progressing.
Insect bites can be irritating and painful. However, most people require little or no treatment as they generally get better on their own. Cleaning the area and applying a cold compress may help in the first instance. A simple painkiller may also be helpful, while a mild corticosteroid cream may reduce swelling. For a larger local reaction, a non-drowsy antihistamine is advised.