An allergy is defined as the immune system overreacting to a harmless substance like pollen or a food protein. While many allergic responses are mild, such as sneezing or a rash, severe reactions directly affect the respiratory system. Low oxygen levels are measured by oxygen saturation (SpO2), which tracks oxygen-carrying hemoglobin in the blood. Mild allergies rarely impact SpO2, but systemic and severe allergic events can cause a significant drop in oxygen levels, a condition known as hypoxia.
How Allergic Reactions Affect Breathing
The link between an allergic reaction and breathing difficulties begins with mast cells. Upon exposure to an allergen, these immune cells release powerful chemical messengers, primarily histamine, into the surrounding tissues, initiating an inflammatory cascade.
Histamine acts directly on the airways, leading to three major physical changes that restrict airflow. It causes the smooth muscles surrounding the bronchial tubes to contract (bronchospasm) and increases vascular permeability, resulting in swelling (edema) of the airway lining.
The inflammatory process also triggers excessive production of thick mucus within the lungs and airways. This combination of muscle constriction, tissue swelling, and mucus accumulation significantly reduces the diameter of the air passages. When airways are narrowed, the body struggles to efficiently move oxygen into the tiny air sacs (alveoli) for exchange with the bloodstream.
Specific Allergic Conditions That Can Lower Oxygen
Two allergic conditions pose the highest risk for oxygen deprivation: allergic asthma and anaphylaxis. Asthma attacks are frequently triggered by common allergens, such as pet dander or dust mites. During an attack, the heightened sensitivity of the airways results in severe and prolonged bronchospasm that can persist despite medication.
This sustained narrowing of the lower airways traps air in the lungs and prevents fresh oxygen from reaching the blood effectively. Allergic asthma is a chronic condition where recurrent exposure can lead to acute episodes of hypoxia.
Anaphylaxis is a life-threatening, multi-system allergic reaction that causes a rapid drop in oxygen levels. The reaction can quickly cause severe swelling of the throat and larynx (laryngeal edema), obstructing the upper airway. Simultaneously, systemic bronchospasm constricts the lower airways, compounding the breathing difficulty. This dual obstruction creates a medical emergency where oxygen levels can fall dangerously low within minutes.
Signs of Low Oxygen (Hypoxia)
Recognizing the signs of hypoxia is important during a severe allergic episode. A person experiencing low oxygen may exhibit significant shortness of breath or rapid, shallow breathing. Other symptoms include restlessness, anxiety, or confusion, which indicates the brain is not receiving sufficient oxygen.
Physical signs include a rapid heart rate, as the heart works harder to circulate the limited oxygen supply. In severe cases, a bluish discoloration of the skin, lips, or nail beds, termed cyanosis, may become noticeable. A pulse oximeter, a small device placed on the finger, measures blood oxygen saturation (SpO2). For a healthy individual, a reading consistently below 90% is considered a medical concern.
Medical Intervention and When to Seek Help
Any allergic reaction involving difficulty breathing or throat tightness requires immediate attention. If symptoms progress rapidly or include wheezing, hoarseness, difficulty swallowing, or fainting, emergency services must be called. Prompt action is necessary because severe airway swelling or bronchospasm can worsen quickly.
For individuals with a known severe allergy, the immediate injection of an epinephrine auto-injector (EpiPen) is the primary step. Epinephrine works rapidly to relax the airway muscles and reduce the swelling that obstructs breathing. Even after administering epinephrine, proceeding to an emergency room for observation and further treatment is necessary. Medical personnel can provide supplemental oxygen, intravenous corticosteroids to reduce inflammation, and inhaled bronchodilators to open the airways further.