Hay Fever & Allergy Season: Why It Can Affect Blood Glucose

Allergy season doesn’t just mean a bit of sneezing, for families living with Type 1 Diabetes, it can quietly affect glucose levels too.

Depending on where you live (and what’s growing nearby), allergy season can begin as early as March and stretch right through to September bringing an unexpected challenge of higher, harder to explain glucose levels.

What Happens in the Body During Allergy Season?

Seasonal allergies (also known as hay fever or allergic rhinitis) occur when the immune system overreacts to triggers like:

• Tree pollen (early spring)

• Grass pollen (late spring/ summer)

• Weed pollen (late summer/ autumn)

• Mould spores (autumn/ winter)

When exposed, the body releases histamine and other inflammatory chemicals to “fight” the allergen.

This immune response causes:

• Nasal congestion

• Runny nose

• Itchy eyes

• Fatigue

• Headaches

• Sinus pressure

But importantly for those with T1D….

It also creates inflammation.

Inflammation & Blood Glucose: The Hidden Link

Inflammation is a form of physical stress on the body.

When the body is under stress, whether from illness, infection, emotional stress, or allergies, it releases stress hormones such as cortisol and adrenaline.

These hormones:

• Increase insulin resistance

• Signal the liver to release stored glucose

• Make glucose levels harder to stabilise

So during allergy season, you might notice:

• Higher than usual readings

• Glucose rising without food

• More correction doses needed

• Increased overnight levels

• “Sticky highs” that are slow to respond

For children and teens especially, this can feel frustrating and confusing when food intake hasn’t changed.

Find out more on how sniffles to stress to teething and lack of sleep can cause inflammation and affect BG levels here “The Sneaky T1D BG Level Saboteur: Inflammation”.

Allergy Medication

Many families rely on antihistamines during hay fever season.

Common options available over the counter include:

• Cetirizine (often sold as Piriteze)

• Loratadine (often sold as Clarityn)

• Fexofenadine (available OTC in recent years)

These are generally glucose neutral for most people.

However, be mindful of:

• Decongestants containing pseudoephedrine

• Steroid nasal sprays (occasionally may slightly elevate glucose in some individuals)

• Oral steroids (can significantly increase glucose levels)

If steroid tablets are prescribed, expect noticeable rises and adjust insulin with your healthcare team’s guidance.

Why This Can Be Especially Tough for Toddlers & Children with T1D

Toddlers & Children may:

• Struggle to describe allergy symptoms

• Feel more tired (which can mask hypo symptoms)

• Eat less due to congestion or feeling unwell

• Sleep poorly, affecting glucose stability

And poor sleep alone can increase insulin resistance the next day.

So allergy season can quietly layer multiple glucose raising factors at once.

Practical Ways to Support Glucose Stability During Allergy Season

1. Watch for Patterns

If you notice unexplained highs around the same time each year, consider allergies as a possible cause.

Tracking:

• Pollen forecasts

• Symptoms

• Glucose trends

Can help you anticipate patterns next season.

2. Preemptive Insulin Adjustments (if needed)

Some families find:

• Slight temporary basal increases help

• A small adjustment to correction factors

• Bring more proactive with earlier corrections

Always adjust gradually and safely.

3. Reduce Allergen Exposure at Home

Simple changes can lower the inflammatory load:

• Shower after being outdoors

• Change clothes after school

• Keep windows closed during high pollen days

• Wash bedding more frequently

• Use air purifiers, if possible

Less allergen exposure = less inflammation = potentially steadier glucose.

4. Support the Immune System Naturally

• Stay well hydrated

• Prioritise sleep

• Encourage anti-inflammatory foods:

  • Oily fish

  • Berries

  • Leafy greens

  • Nuts and seeds

While food won’t “cure” allergies, reducing overall inflammation can support better glucose stability.

5. Monitor Overnight Levels

Inflammation often causes subtle overnight rises.

If you use CGM, look for:

• Gradual early morning climbs

• Increased dawn phenomenon

Small basal tweaks (if appropriate) may help smooth this.

6. Prioritise Sleep

Blocked noses = broken sleep = higher glucose the next day.

Simple tools:

• Saline nasal sprays

• Air purifiers

• Antihistamine timing in the evening

Better sleep supports better glucose stability.

7. Stay Hydrated

Higher glucose + antihistamines can increase dehydration risk.

Encourage steady fluid intake, especially on warm sunny days.

8. Don’t Ignore Fatigue & Mood Changes

Higher glucose plus poor sleep plus allergy symptoms can impact mood significantly, especially in teens.

If you’re seeing:

• Irritability

• Emotional sensitivity

• Difficulty concentrating

It may not be “behaviour”, it may be inflammation + glucose fluctuations.

The Emotional Side

Spring and summer should feel carefree, but fluctuating glucose during allergy season can knock confidence.

If numbers feel stubborn:

It might not be the carbs.

It might not be growth.

It might not be hormones.

It might be pollen.

Understanding the inflammation link removes blame and helps you respond calmly and strategically.

Final Thoughts

Living with T1D means becoming a detective.

Allergy season is just another variable in the puzzle.

By:

• Watching patterns

• Supporting the immune system

• Making small insulin adjustments when needed

• Reducing exposure where possible

You can ride the seasonal allergy wave, rather than being knocked over by it.