Peanut allergy is a public health concern which affects a significant proportion of the population. Accidental exposure to peanut can cause severe and fatal reactions in peanut allergic individuals and currently their only safeguard is to practise careful avoidance. Identification and protection of at-risk members of the allergic population is critical in managing this life-threatening condition. This thesis produces key data to enable this. A prospective study was performed on 60 peanut allergic participants to determine thresholds of reactivity to peanut using oral challenges with incrementally increasing amounts of peanut protein. Following a double-blind placebo-controlled peanut challenge, participants received three further peanut challenges, two with co-factors: sleep deprivation and exercise, and one without. Severity was measured using a numerical scale derived from symptoms and serum tryptase was measured at each challenge. A total of 187 challenges were performed. Findings were that the median amount of peanut protein which induces a reaction in 10% of the population (ED10) was 12.3mg (95% CI 7.3,20.4) equivalently this suggests that 90% of the allergic population will not react to doses below this level. Both sleep deprivation and exercise have a significant effect on lowering reaction threshold (ED10), by 5 times and 2.5 times respectively. Separately there is a reduction in threshold with successive challenges. Co-factors also significantly increased symptom severity during challenge reactions. In particular sleep deprivation significantly increased the severity of gastrointestinal symptoms suggesting that a stressful stimulus may affect intestinal permeability. Evidence was provided for the importance of asthma as a risk factor which increased the severity of respiratory symptoms during reaction. Using a novel visual analogue scale for measuring the participant’s perception of severity, a poor correlation was observed between the participant’s perception of the reaction and the overall numerical severity score, suggesting that participants misperceive severe symptoms. This thesis provides the first data showing that symptom patterns in repeated challenges show a high degree of homogeneity within individuals, but importantly that this symptom homogeneity is also observed across individuals. Lastly the utility of serum tryptase in identifying food allergic reactions has been disputed previously. This thesis provides evidence of its value and identifies a rise cut-off of 30% as being diagnostic of a food allergic reaction, but cautions that acute levels must be compared with baseline as this rise may occur within the normal range.