When to Start Hay Fever Treatment and How Long It Takes to Work

In short: Timing makes a big difference to hay fever control. Start a steroid nasal spray one to two weeks before your usual symptoms begin, because it takes several days to reach full effect. Non-drowsy antihistamines start working within hours. Keep treatment going every day until your pollen season ends, which for most people in the UK is somewhere between late March and September.

This guide, written by a Ready Health prescribing pharmacist, explains how to time your hay fever treatment around the UK pollen seasons.

When is hay fever season in the UK?

The Met Office describes three main pollen phases. Which one affects you depends on what you are allergic to:

Seasons vary from year to year with the weather, and grass pollen can start earlier after a warm spring. If your symptoms begin at the same time each year, note the date: it is the best guide to when you should start treatment.

How long do hay fever treatments take to work?

Why should I start before symptoms begin?

Once pollen has triggered inflammation in the nose, it takes longer to calm it down. Starting a steroid spray before the season means it is already working when pollen levels rise. Asthma + Lung UK suggests starting nasal steroids one to two weeks before your symptoms usually start, and some antihistamines two to four weeks before.

How long should I keep using treatment?

Continue daily until your usual pollen season has finished, then stop. There is no need to taper steroid nasal sprays or antihistamines. If you need treatment all year round, speak to a pharmacist or GP: year-round symptoms may be caused by dust mites, pets or a non-allergic form of rhinitis.

Why not a single long-acting treatment for the whole season?

People sometimes look for one treatment to cover the whole season. Long-acting steroid injections are not licensed for hay fever in the UK and are not recommended in UK guidance. Because the medicine acts throughout the body for several weeks and cannot be removed once given, risks include dents in the skin at the injection site, raised blood sugar, mood and sleep changes, suppression of the body's own steroid hormones and, with repeated use, bone thinning. Daily first-line treatment, started early, is the safer and evidence-based approach.

Frequently asked questions

Is it too late to start a nasal spray once symptoms have begun?

No. It will still help, but it may take a little longer to reach full effect. An antihistamine can provide quicker relief in the meantime.

Do I need to take antihistamines every day?

For mild symptoms you can take them when needed. If you have symptoms most days, regular daily use usually gives better control.

When should I start immunotherapy?

Immunotherapy is started by a specialist, usually several months before the pollen season, and continued for around three years. A GP or prescriber can discuss whether referral is appropriate.

How do I know when pollen levels are high?

Check the daily pollen forecast from the Met Office, which shows levels across the UK.

Key takeaways

• Know which pollen season affects you: tree, grass or weed.
• Start steroid nasal sprays one to two weeks before symptoms usually begin.
• Antihistamines work within hours; steroid sprays build up over days.
• Use treatment daily until your season ends.
• Year-round symptoms need a review, as they may not be hay fever.

Sources and further reading

• Met Office: UK pollen seasons
• Asthma + Lung UK: Hay fever treatments
• NHS: Hay fever

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

If you would like help planning your treatment before the next pollen season, you can book a hay fever consultation at Ready Health in Standish, Wigan. A prescriber will review your symptoms and current treatment and explain suitable options. Any prescription is only issued if a prescriber decides it is clinically appropriate.