Peanut allergy: what happens in the body?
In a peanut allergy, IgE antibodies wrongly recognize a peanut protein: mast cells then suddenly release histamine and other substances, which make the skin swell, tighten the airways and let fluid leak out of the blood vessels. In the United States, 2.2% of children are thought to be affected, according to their parents (Gupta, 2018).
Simplified diagram of a severe reaction. Severity and timing vary widely from one person and one reaction to another. Relative levels: each curve has its own scale. All curves are estimates, drawn from the studies cited.
What happens, step by step?
Drawing not to scale. Blood pressure, bpm and breathing: estimates to illustrate the mechanisms, not measurements.
Frequently asked questions
How can someone react without ever having eaten peanut?
The priming can happen without a meal. In a 2015 study, children exposed to more peanut protein in household dust were more often sensitized, especially if they had eczema. The authors see this as a plausible route through damaged skin (Brough, 2015).
How much peanut triggers a reaction?
It varies from person to person, and sometimes very little is enough. A dose of 1.5 mg of protein, about 6 mg of peanut, caused an objective reaction in 8 of 378 allergic children, all mild (Hourihane, 2017).
Why does blood pressure drop?
Because the vessels widen and let fluid out. Up to 35% of this fluid can leave the vessels in 10 minutes, a figure that appears to come from reactions under anesthesia and may not apply to a food. Less blood returns to the heart, so it pumps out less (Nuñez-Borque, 2022).
Why does epinephrine work where an antihistamine falls short?
Epinephrine acts on several receptors at once: it tightens the vessels, strengthens the heart and opens the airways (Reber, 2017). An antihistamine targets only the H1 histamine receptor and, as a pill, takes at least 1 to 2 hours to work (Sheikh, 2007).
Can a reaction come back after it has calmed down?
Yes, sometimes: this is called a biphasic reaction. Across 27 studies, 192 of 4,114 people, about 4.7%, had this second wave, a median of 11 hours after the first. It was less common when a food was the cause (Lee, 2015).
True or false?
Roasting peanuts makes them less allergenic.
False. In the lab, roasted peanuts bound about 90 times more IgE than raw peanuts (Maleki, 2000). Boiled or fried, they bound less than roasted ones (Beyer, 2001).
Having IgE against an allergen is always enough to cause a reaction.
False. Many people have specific IgE in their blood with no symptoms at all: IgE is a risk factor, not proof of a reaction (Reber, 2017).
Smelling or touching peanut butter caused severe reactions in a study of allergic children.
False. Among 30 very allergic children, none had a systemic or respiratory reaction. Skin contact caused only a local reaction in some. The study is small and does not apply to eating peanut (Simonte, 2003).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
How does the reaction unfold, minute by minute?
A severe reaction often follows this order, but timing varies widely. Some reactions stop on their own, others get worse: this curve shows just one.
| Minutes after eating peanut | Substances released | Patches on the skin | Tight airways | Blood pressure | What happens |
|---|---|---|---|---|---|
| 0 min | 0 | 0 | 0 | 85 | Peanut is eaten |
| 30 min | 88 | 57 | 25 | 80 | +30 min after eating peanut |
| 60 min | 48 | 83 | 71 | 35 | +60 min after eating peanut |
| 90 min | 21 | 71 | 71 | 31 | +90 min after eating peanut |
| 120 min | 10 | 55 | 65 | 30 | +120 min after eating peanut |
Key points
- Often around 30 minutes (Throughout, Shown in humans)
In supervised tests in 1,610 children, the first symptoms to peanut came a median of 30 minutes after the first dose, most often between 14 and 45 minutes (Kojima, 2026). Source: Kojima et al., "Timing of symptom onset during 60-min interval oral food challenges in children," Allergol Int, 2026 - A rapid leak (Throughout, Shown in humans)
Up to 35% of the fluid can leave the vessels in 10 minutes, a figure that appears to come from reactions under anesthesia (Nuñez-Borque, 2022). Source: Nuñez-Borque et al., "Pathophysiological, Cellular, and Molecular Events of the Vascular System in Anaphylaxis," Front Immunol, 2022 - Curves: estimate (Throughout, Hypothesis)
Levels are relative, each curve has its own scale. They illustrate the order of events, not a measurement. Source: Reber, Hernandez and Galli, "The pathophysiology of anaphylaxis," J Allergy Clin Immunol, 2017
What does epinephrine change on these curves?
Example with an injection at 40 minutes. The peak in the blood comes within minutes: the vessels tighten, the airways open, blood pressure rises.
| Minutes after eating peanut | Blood pressure, without epinephrine | Blood pressure, with epinephrine | Airways, without epinephrine | Airways, with epinephrine | What happens |
|---|---|---|---|---|---|
| 0 min | 85 | 85 | 0 | 0 | Peanut is eaten |
| 30 min | 80 | 80 | 25 | 25 | +30 min after eating peanut |
| 60 min | 35 | 82 | 71 | 18 | +60 min after eating peanut |
| 90 min | 31 | 78 | 71 | 20 | +90 min after eating peanut |
| 120 min | 30 | 74 | 65 | 22 | +120 min after eating peanut |
Key points
- 8 minutes (Throughout, Shown in humans)
In 8 children, the peak in the blood came at 8 minutes on average when given into muscle, versus 34 minutes under the skin in 9 others (Simons, 1998). Source: Simons et al., "Epinephrine absorption in children with a history of anaphylaxis," J Allergy Clin Immunol, 1998 - Three receptors (Throughout, Shown in humans)
Alpha-1 on the vessels, beta-1 on the heart, beta-2 on the airways (Reber, 2017). Source: Reber, Hernandez and Galli, "The pathophysiology of anaphylaxis," J Allergy Clin Immunol, 2017 - Curves "with": estimate (Throughout, Hypothesis)
The recovery varies with the person and the timing of the injection; a second wave is still possible (Lee, 2015). Source: Lee et al., "Time of Onset and Predictors of Biphasic Anaphylactic Reactions," J Allergy Clin Immunol Pract, 2015
What does an antihistamine alone change on these curves?
Example with a pill at 40 minutes. The skin may improve, but slowly. No effect is expected on the airways or blood pressure.
| Minutes after eating peanut | Skin, without medication | Skin, with antihistamine | Airways, unchanged | Blood pressure, unchanged | What happens |
|---|---|---|---|---|---|
| 0 min | 0 | 0 | 0 | 85 | Peanut is eaten |
| 30 min | 57 | 56 | 25 | 80 | +30 min after eating peanut |
| 60 min | 83 | 77 | 71 | 35 | +60 min after eating peanut |
| 90 min | 71 | 65 | 71 | 31 | +90 min after eating peanut |
| 120 min | 55 | 46 | 65 | 30 | +120 min after eating peanut |
Key points
- At least 1 to 2 hours (Throughout, Shown in humans)
As a pill, absorption and effect are slow (Sheikh, 2007). Source: Sheikh et al., "H1-antihistamines for the treatment of anaphylaxis with and without shock," Cochrane Database Syst Rev, 2007 - No direct measurement (Throughout, Hypothesis)
The 2007 review found no trial meeting its criteria: these curves follow the expected mechanism, not a trial result. Source: Sheikh et al., "H1-antihistamines for the treatment of anaphylaxis with and without shock," Cochrane Database Syst Rev, 2007
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