You developed asthma as an adult. Your genes may explain why.

Your airways have tiny receptors on the smooth muscle that lines them. When you use a beta-2 agonist inhaler (albuterol or similar), it binds to these receptors and tells the muscles to relax, opening your airways. The ADRB2 gene codes for the structure and sensitivity of these receptors.

The Arg16Gly variant of ADRB2 is present in roughly 40% of the population. When you carry the Gly allele, your beta-2 receptors are less responsive to the medication. This means your rescue inhaler may not work as effectively as it should, and you might experience repeated exacerbations despite using your inhaler correctly.

You might notice that your inhaler works brilliantly on some days and barely touches your symptoms on others. You might find yourself using your rescue inhaler more frequently than your doctor expects. You might feel like you are not responding to standard asthma medications the way you are supposed to.

Interleukin-4 is a immune signaling molecule that tells your T cells and B cells to mount an allergic response. High IL-4 pushes your immune system into a Th2-skewed state, which means it defaults to producing IgE antibodies in response to inhaled allergens and other triggers. Normal IL-4 levels are fine. Too much is a problem.

The IL4 promoter variant at position -590 C>T is carried by roughly 30% of the population. When you have the T allele, your cells produce more IL-4. More IL-4 means higher IgE levels, stronger allergic responses to common triggers, and greater airway inflammation in response to allergens.

You might notice that you react to things other people ignore: dust, pet dander, pollen, mold spores. Your reactions seem disproportionate to the exposure. You might have a history of eczema or hay fever that preceded your asthma diagnosis. Your asthma may be worse during certain seasons or in certain environments. You might struggle with food sensitivities as well.

Interleukin-13 is the key driver of allergic airway inflammation. It tells your immune cells to flood your airways with eosinophils, stimulates mucus-producing cells, and triggers airway remodeling (thickening of the airway walls). Normal IL-13 signaling is part of healthy immune responses. Dysregulated IL-13 is asthma.

IL13 variants are present in roughly 30 to 35% of the population. When you carry a variant that increases IL-13 production or signaling, your airways are chronically primed for inflammation. You develop eosinophilic airway infiltration, excessive mucus production, and structural changes to your airway walls that make them permanently more sensitive to triggers.

You might experience persistent cough, especially at night or after exposure to triggers. Your chest might feel heavy or congested. You might produce thick mucus when you cough. Your asthma may not respond well to standard controller medications and may require escalation to biologic therapy. Infections seem to trigger longer, more severe exacerbations.

Filaggrin is a protein that glues together the outermost cells of your skin and airways, creating a tight physical barrier. This barrier is your first line of defense: it keeps allergens out and prevents them from triggering immune activation. When filaggrin is working properly, allergens stay on the surface. When it is not, they penetrate deep into your tissue.

FLG mutations like R501X and 2282del4 are present in roughly 10% of people with European ancestry, but prevalence is much higher in other populations. When you carry a FLG mutation, your airway barrier is structurally weak; allergens penetrate deeply, your immune system sees them, and allergic sensitization happens.

You might have a history of eczema or dry skin that preceded your asthma. You might notice that your skin reacts easily to irritants, fragrances, or detergents. Your asthma often flares during low-humidity seasons or after exposure to irritants like perfume, smoke, or dust. You may also have hay fever or other allergic conditions. The pattern is sometimes called the atopic march: eczema in childhood, hay fever in adolescence, asthma in adulthood.

GSTM1 codes for a enzyme that neutralizes reactive oxygen species (ROS) and detoxifies pollutants, cigarette smoke, and other environmental toxins before they damage your airway cells. This enzyme is especially important in the lungs, which are directly exposed to inhaled irritants. A working GSTM1 means your airways can handle oxidative stress. A non-functional GSTM1 means they cannot.

The GSTM1 null deletion is present in roughly 40 to 50% of the population depending on ancestry. If you carry the null allele, your airways have little to no GSTM1 enzyme activity; you accumulate oxidative damage more rapidly, and your airways become chronically inflamed and hyperreactive.

You might notice that your asthma flares during high air pollution days or after exposure to smoke, strong fragrances, or chemical irritants. Your lungs may feel irritated by things that do not bother other people. You might have a history of reactive airways triggered by air quality changes. Your asthma exacerbations may be more frequent during winter (when heating increases indoor pollution) or summer (when ozone levels are high).

The VDR gene codes for the vitamin D receptor, a protein that vitamin D binds to in order to regulate immune function. Vitamin D is not just a vitamin; it is a hormone that tells your immune system to be tolerant or reactive. When VDR is working well and vitamin D levels are adequate, your immune system stays balanced. When VDR function is impaired, your immune system defaults to reactive and inflammatory.

VDR variants like the FokI polymorphism are present in the majority of the population. Certain variants reduce VDR sensitivity to vitamin D signaling. This means you need more vitamin D to achieve the same immune-regulating effect, and chronically low vitamin D makes your asthma worse.

You might find that your asthma is seasonal, worse in winter when vitamin D levels drop. You might have low or low-normal vitamin D levels despite reasonable sun exposure. You might notice that supplementing with vitamin D actually improves your asthma control and reduces exacerbations. Your asthma may be associated with other conditions linked to vitamin D deficiency, like osteoporosis or mood changes.