Allergies: Vitamin C and Quercetin Can Help

Vitamin C and quercetin are both antioxidant compounds, and both have been studied in relation to how immune cells behave. Vitamin C contributes to the normal function of the immune system and to the protection of cells from oxidative stress. Quercetin is a plant flavonoid examined in laboratory research on histamine release from immune cells. Neither is a treatment, and research in this area is still developing.

Air quality and the body's response

Fine particulate matter (PM2.5), household dust, pollen, mold spores and pet dander are airborne particles the body meets every day, and in cities they rise and fall with traffic, weather and season. The immune system recognizes some of these as foreign material. Signs people commonly notice include a runny or blocked nose, sneezing, itchy or watery eyes, a scratchy throat and itchy skin. How much any individual notices varies widely, and is influenced by genetics, time spent in poorly ventilated air-conditioned rooms, and outdoor air quality. Persistent or severe signs, or anything affecting breathing or sleep, should be assessed by a qualified healthcare provider rather than self-managed with supplements.

Histamine is normal signaling

Histamine is a signaling molecule the body makes and stores, largely in cells called mast cells. When mast cells are activated they release histamine, which increases local blood flow and makes small blood vessels more permeable. The blood vessels of the nose and airways carry a high density of mast cells, which is why those are the areas where people tend to notice a response first. Histamine is not a harmful substance in itself: it also has normal roles in gastric acid secretion and in regulating wakefulness.

What vitamin C does in the body

Vitamin C, or ascorbic acid, is a water-soluble essential nutrient. Humans cannot make it, so it has to come from food or supplements every day. Its established roles include contributing to normal collagen formation for the normal function of skin, blood vessels, cartilage and bones; contributing to the normal function of the immune system; protecting cells from oxidative stress; contributing to normal energy-yielding metabolism; and increasing the absorption of non-heme iron. Vitamin C has also been studied in relation to histamine metabolism, and that line of research is ongoing.

Vitamin C from acerola cherry, and isolated ascorbic acid

Acerola cherry (Malpighia emarginata) is among the most vitamin-C-dense fruits known. Vitamin C sourced from acerola arrives alongside the fruit's other naturally occurring compounds rather than as a single isolated molecule, and that is why many formulations choose a fruit-derived source: the goal is a composition closer to what is found in food. Isolated ascorbic acid is well characterized and widely used, and the difference between the two is composition, not quality. Formulations also differ in acidity, which is one reason some people prefer fruit-derived or buffered forms.

Plant compounds naturally present in acerola cherry include:

• Bioflavonoids, polyphenols that show antioxidant activity in laboratory assays
• Carotenoids, including beta-carotene, which the body converts to vitamin A as needed
• Anthocyanins, the red-purple pigments common to many berries
• Lutein and zeaxanthin, carotenoids that accumulate in the retina and contribute to its normal pigment composition

How much, and how to take it

The Thai RDI for vitamin C is 100 mg per day. Because vitamin C is water-soluble, the body does not build large stores of it and surplus intake is excreted in urine, so regular daily intake matters more than any single large amount. People taking more than the RDI commonly divide it across the day rather than taking it all at once, and some find a large single amount less comfortable on an empty stomach. If you take prescription medication or have a kidney condition, check with a qualified healthcare provider before starting any supplement.

What quercetin is

Quercetin is a flavonoid, one of the plant pigments that give fruits, flowers and vegetables their color. Dietary sources include onions (particularly red onions), apples with the skin on, capers, kale, broccoli, berries, buckwheat, and black and green tea. In vitro, quercetin acts as an antioxidant, meaning it can neutralize free radicals, the reactive particles that damage cell membranes and interfere with DNA. Laboratory studies have also examined how quercetin affects histamine release from immune cells, which is why researchers have taken an interest in it.

Quercetin has been studied in humans as well. One published example is a randomized, double-blind, placebo-controlled trial in 66 adults aged 22 to 78 who were sensitive to pollen; participants took either 200 mg of quercetin daily or a placebo for four weeks, with validated quality-of-life questionnaires and visual analog scales recorded before and after. No serious adverse effects were reported during the study. Human evidence overall remains limited, and quercetin is not a substitute for medical care.

Ingredients often formulated alongside them

Spectra is a standardized blend of extracts from 24 fruits, vegetables and herbs, characterized in laboratory assays for its content of plant compounds including polyphenols, anthocyanins and carotenoids. It appears in formulations as a concentrated source of plant compounds for people whose daily fruit and vegetable intake varies. Vitamin D3, or cholecalciferol, is the form the skin produces on sun exposure and the form most used in supplements; it contributes to the normal function of the immune system, to normal muscle function, and to the maintenance of normal bones and teeth through its role in calcium and phosphorus absorption. People who spend most of the day indoors, or who cover up outdoors, typically get less of it from sunlight.

Air quality is largely outside individual control, but nutritional status is not. Meeting daily vitamin C needs, eating a varied range of plant foods, ventilating indoor spaces and getting consistent sleep are all reasonable steps. For anything persistent, see a qualified healthcare provider.