Peanut Allergy

Peanut allergy is the main cause of anaphylaxis due to food allergy.

Peanut allergy develops when the body's immune system has an abnormal, hypersensitivity response to one or more of the peanut proteins. It is one of the most common food allergies in both children and adults. It receives particular attention because it is relatively common, typically lifelong, and can cause severe allergic reactions.

Peanut allergy is the leading cause of anaphylaxis and death due to food allergy. It can lead to a significant burden on patients and their families. Peanut is a common food ingredient making strict avoidance difficult. Therefore, there is a relatively high rate of accidental peanut ingestion for those trying to avoid peanuts. For all of the above reasons, peanut allergy has become an important public health issue.

This prevalence of peanut allergy has increased significantly over the past decade, most notably in Westernized countries. The prevalence of peanut allergy in Westernized countries is approximately 0.5%, with the greatest prevalence in children under 3 years of age. This increase in prevalence has also occurred with other allergic conditions, such as eczema (atopic dermatitis), asthma, and hay fever (allergic rhinitis).

Peanut allergy is much less common in underdeveloped areas of the world, such as Africa and Asia. Emerging literature suggests that the increasing rate of peanut allergy may be leveling off in many nations, including the United States.

Risk factors for peanut allergy include a personal or family history of allergic conditions, such as:

• Asthma
• Hay fever (allergic rhinitis)
• Particularly eczema (atopic dermatitis)

A sibling of a child with a peanut allergy has approximately a 7% chance of developing peanut allergy, as compared to the baseline population risk of 0.5%. Other factors influencing peanut allergy include exposure during pregnancy and lactation, exposure to peanut protein through household dust, and exposure to skin-care products containing crude peanut oil.

There has been significant recent research on the timing of peanut exposure in a child's diet and its effect on the risk of allergy. In the early 2000s, recommendations were to delay the introduction of peanuts until 3 years of age. The rates of peanut allergy more than doubled in countries following these recommendations. It was also observed that rates of peanut allergy were significantly lower in countries, such as Israel, where children were introduced to peanuts at a younger age.

In 2008, the recommendation regarding the delayed introduction of peanuts was retracted, and research began to indicate that earlier introduction of peanuts may be protective against food allergies. In a landmark study published in 2015 (LEAP study), it was shown that early introduction of peanuts into a child's diet, at 4 months of age, significantly decreased the risk of developing peanut allergy in a high-risk population. This study, along with additional research, may very well lead to updated guidelines on the timing of the introduction of peanuts and other highly allergenic foods into a child's diet.

It is not clear why the rate of peanut allergy is increasing in the United States and other Westernized nations. This is an area of active medical research.

The most important step in the diagnosis of peanut allergy is a detailed history. A good history may essentially make the diagnosis of a peanut allergy. Important factors for a suggestive history of peanut allergy include the following:

Timing of symptoms

The majority of reactions occur within 20 minutes, with nearly all reactions occurring within two hours of exposure to peanuts.

Types of peanut allergy symptoms

About 80% to 90% of reactions involve skin manifestations such as:

• A rash, including hives
• Redness
• Itching

Nevertheless, reactions can occur in the absence of a rash, and these reactions may be the most severe.

Other common signs and symptoms involve the following:

• Respiratory system (difficulty breathing, coughing, wheezing)
• Gastrointestinal system (nausea, vomiting, diarrhea)
• Cardiovascular system (increased heart rate, decreased blood pressure)
• Neurological system (lightheadedness, passing out)
• Even changes in behavior, especially in children

Consistency

Reactions should consistently occur with every peanut exposure.

Following the history, the skin prick test (SPT) is generally the test of choice in making a diagnosis of peanut allergy. It is very important to be aware that a positive SPT alone does not make the diagnosis of peanut allergy. Of note, many individuals with a positive SPT to peanuts will not be peanut allergic. The usefulness of a peanut SPT increases as the size of the reaction increases. Sometimes, SPT results are inconclusive and may be followed up with a blood test known as peanut-specific IgE levels.

Similar to the SPT, peanut-specific IgE levels must be interpreted based on the clinical history. Undetectable peanut-specific IgE levels do not rule out the possibility of peanut allergy, with reaction rates of up to 20% being reported in individuals with undetectable peanut-specific IgE. Much like SPT, the likelihood of true peanut allergy increases with increasing levels of peanut-specific IgE.

Despite a thorough clinical history, SPT, and peanut-specific IgE levels, the diagnosis of peanut allergy may remain in question. In these instances, a physician-supervised oral food challenge (OFC) may be indicated. In an OFC, patients are given gradually increasing amounts of peanuts, usually in an allergist's office, and closely monitored for allergic symptoms. OFCs have not only been shown to significantly improve quality of life regardless of whether the challenge is passed or failed but they have also been shown to be very safe when performed in an appropriate setting under the supervision of a physician experienced in the management of food allergy. During the diagnostic process of peanut allergy, it is also important to determine if peanut-allergic individuals are allergic to tree nuts, since up to one-third of patients with peanut allergy will also react to tree nuts.

Strict avoidance of peanuts and prompt treatment of accidental ingestions are the mainstays of management of peanut allergy. The goals of treatment are to minimize the risk of accidental ingestion while maintaining adequate nutrition and an acceptable quality of life.

Although there is significant research focused on oral immunotherapy and desensitization protocols for peanut allergy, these treatment options are still not ready for widespread clinical use. There is also significant research involving a peanut patch, also known as epi-cutaneous immunotherapy.

Early studies of this patch have shown that by applying a patch containing peanut protein to the skin, it may be possible to make peanut-allergic individuals less sensitive to peanut protein and it may protect certain peanut-allergic individuals from experiencing a reaction to accidental peanut exposure. There are still many questions regarding this possible form of therapy and it is still not ready for widespread clinical use.

Peanut is a common food in the United States, and strict avoidance requires constant awareness of food labels and food ingredients. United States legislation requires all food companies to identify on labels whether their products contain the most common food allergens, including peanuts.

Advisory labeling practices, such as those stating "may contain peanut," "manufactured on shared equipment with peanut," or "manufactured in the same facility as peanut," are not regulated. The potential risk of ingesting peanuts from foods labeled with advisory labeling is unknown, so peanut-allergic individuals should also avoid these foods.

Despite attempts at strict avoidance, accidental ingestions occur in up to 15% of patients per year, as evidenced by a British study. All individuals with a peanut allergy should have an emergency action plan outlining the treatment plan for an acute reaction. Since epinephrine injection is the only treatment for a significant allergic reaction, all individuals with a peanut allergy should carry an epinephrine auto-injector (Auvi-Q, Epipen, Twinject) at all times.

Although antihistamines such as diphenhydramine (Benadryl) may also be used in the management of acute allergic reactions, epinephrine generally remains the treatment of choice. Individuals who experience an acute allergic reaction to accidental peanut exposure should also notify a healthcare professional. It is very important to note that the severity of acute reactions is variable and cannot be predicted by diagnostic testing or previous reactions. Risk factors for poor outcomes from peanut allergy include asthma and delayed treatment with epinephrine.

There are important additional considerations in managing and counseling individuals with peanut allergy. Research has shown that reactions due to skin contact are typically limited to the site of contact and unlikely to cause a systemic reaction or anaphylaxis. Similarly, the vast majority of peanut-allergic individuals will tolerate being around peanuts and the smell of peanuts, since peanut protein is not airborne.

The majority of peanut-allergic individuals will also tolerate peanut oil, since the peanut protein is not present in the highly purified oils, except in the rarer cold-pressed oils. Although peanut is a legume, most peanut-allergic individuals will also tolerate other legumes, such as soy, peas, and green beans. Exposure to peanuts through another person's saliva (such as from kissing) has been shown to trigger a reaction. All peanut-allergic individuals should discuss these considerations and other questions with their healthcare provider.

Unfortunately, there is no cure for peanut allergy. Although the natural history of peanut allergy is often difficult to predict, peanut allergy can be outgrown. Approximately 20% of children with peanut allergy will tolerate peanuts by their school-age years. Favorable factors to outgrow peanut allergy include smaller SPT at the time of diagnosis, lower specific IgE levels at the time of diagnosis, milder initial reaction to peanuts, and minimal additional allergic conditions, including a lack of additional food allergies (particularly tree nuts). If there is a significant likelihood that a child has outgrown peanut allergy, a physician-supervised oral food challenge can be pursued.