Your question is focusing on contact sensitivity or inhaled exposure in an individual who is tree nut allergic. Although it is difficult to make absolute statements, I am convinced by the available literature and clinical experience that there is no significant risk associated with a tree nut allergic person engaging in activities in close proximity to a tree, even with nuts on the ground around the tree. Certainly skin contact with nuts outside of the shell is a potential risk if common sense measures of avoidance are not in play. Although aerosol food allergen exposure has been described, this has been primarily in cooking of the food. I have cared for a patient who would have respiratory symptoms when sitting in an establishment with peanut shells on the floor, so aerosol exposure is theoretically possible but is not a realistic concern in an outside environment.
In summary, there is risk in any activity of life. I think you can reassure your patient and their family that the risk of playing under a pecan or walnut tree is negligible, even with pecan or walnut allergy, as long as the nuts are not handled or eaten. Inhalation risk is not a concern in this circumstance.
I have attached a couple of references and a prior Ask The Expert question. Please note that peanuts are NOT tree nuts.
Roberts, G., N. Golder, and G. Lack. "Bronchial challenges with aerosolized food in asthmatic, food-allergic children." Allergy 57.8 (2002): 713-717.
Background: Allergic asthma is usually considered to be provoked by aeroallergens. However, we have recently recognized a group of children with food allergies who also develop asthma when exposed to the aerosolized form of the food.
Methods: Between 1997 and 1999 we prospectively identified children with an immunoglobulin (Ig)E-mediated food allergy who develop asthma on inhalational exposure to the relevant food allergen while it is being cooked. Subjects were exposed for 20 min to the aerosolized form of the allergen and the symptoms and the lung function were monitored. Aerosolization was achieved by cooking the food in a small room. Where possible challenges were double-blinded.
Results: We identified 12 children with an IgE-mediated food allergy who developed asthma on inhalational exposure to food. The implicated foods were fish, chickpea, milk, egg or buckwheat. Nine out of the 12 children consented to undergo a bronchial food challenge. Five challenges were positive with objective clinical features of asthma. Additionally, two children developed late-phase symptoms with a decrease in lung function. Positive reactions were seen with fish, chickpea and buckwheat. There were no reactions to the seven placebo challenges.
Conclusions: We have presented a prospective series of children with food allergy who developed symptoms of asthma with exposure to aerosolized food allergens. Our data demonstrates that, as in the case of other aeroallergens, inhaled food allergens can produce both early- and late-phase asthmatic responses. This highlights the importance of considering foods as aeroallergens in children with coexistent food allergy and allergic asthma. For these children, dietary avoidance alone may not be sufficient and further environmental measures may be required to limit exposure to aerosolized food.
Perry, Tamara T., et al. "Distribution of peanut allergen in the environment." Journal of Allergy and Clinical Immunology 113.5 (2004): 973-976.
Background: Patients with peanut allergy can have serious reactions to very small quantities of peanut allergen and often go to extreme measures to avoid potential contact with this allergen.
Objective: The purpose of this study was to detect peanut allergen under various environmental conditions and examine the effectiveness of cleaning agents for allergen removal.
Methods: A monoclonal-based ELISA for Arachis hypogaea allergen 1 (Ara h 1; range of detection, 30-2000 ng/mL) was used to assess peanut contamination on cafeteria tables and other surfaces in schools, the presence of residual peanut protein after using various cleaning products on hands and tabletops, and airborne peanut allergen during the consumption of several forms of peanut.
Results: After hand washing with liquid soap, bar soap, or commercial wipes, Ara h 1 was undetectable. Plain water and antibacterial hand sanitizer left detectable Ara h 1 on 3 of 12 and 6 of 12 hands, respectively. Common household cleaning agents removed peanut allergen from tabletops, except dishwashing liquid, which left Ara h 1 on 4 of 12 tables. Of the 6 area preschools and schools evaluated, Ara h 1 was found on 1 of 13 water fountains, 0 of 22 desks, and 0 of 36 cafeteria tables. Airborne Ara h 1 was undetectable in simulated real-life situations when participants consumed peanut butter, shelled peanuts, and unshelled peanuts.
Conclusion: The major peanut allergen, Ara h 1, is relatively easily cleaned from hands and tabletops with common cleaning agents and does not appear to be widely distributed in preschools and schools. We were not able to detect airborne allergen in many simulated environments.
Can a person who has a serious reaction to ingesting peanuts have a reaction to simply touching peanuts or peanut shells? The individual has an epipen for this allergy but has never used it.
A: The answer to your question is that touching peanuts would be highly unlikely to produce an anaphylactic event in a patient with peanut allergy, as you can see from the abstract copied below from The Journal of Allergy and Clinical Immunology.
Background: Casual skin contact or inhalation of peanut butter fumes is reported and feared to cause allergic reactions in highly sensitive children with peanut allergy but has not been systematically studied.
Objective: We sought to determine the clinical relevance of exposure to peanut butter by means of inhalation and skin contact in children with peanut allergy. Methods: Children with significant peanut allergy (recent peanut-specific IgE antibody concentration >50 kIU/L or evidence of peanut-specific IgE antibody and one of the following: clinical anaphylaxis, a reported inhalation-contact reaction, or positive double-blind, placebo-controlled oral challenge result to peanut) underwent double-blind, placebo-controlled, randomized exposures to peanut butter by means of contact with intact skin (0.2 mL pressed flat for 1 minute) and inhalation (surface area of 6.3 square inches 12 inches from the face for 10 minutes). Placebo challenges were performed by using soy butter mixed with histamine (contact), and scent was masked with soy butter, tuna, and mint (inhalation).
Results: Thirty children underwent the challenges (median age, 7.7 years; median peanut IgE level, >100 kIU/L; 13 with prior history of contact and 11 with inhalation reactions). None experienced a systemic or respiratory reaction. Erythema (3 subjects), pruritus without erythema (5 subjects), and wheal-and-flare reactions (2 subjects) developed only at the site of skin contact with peanut butter. From this number of participants, it can be stated with 96% confidence that at least 90% of highly sensitive children with peanut allergy would not experience a systemic-res- piratory reaction from casual exposure to peanut butter.
Conclusions: Casual exposure to peanut butter is unlikely to elicit significant allergic reactions. The results cannot be generalized to larger exposures or to contact with peanut in other forms (flour and roasted peanuts). (J Allergy Clin Immunol 2003;112:180-2.)
Phil Lieberman, M.D.
I hope this information is of help to you and your patient.
All my best.
Dennis K. Ledford, MD, FAAAAI