Many mild allergies, such as seasonal hay fever, can be managed with advice from a pharmacist and over-the-counter medicines. It is worth seeing a doctor when symptoms are not controlled despite regular use of antihistamines and nasal sprays, when they significantly disrupt sleep, work, or school, or when they keep coming back and you want to know the cause.
You should also see a doctor if you suspect a food or medicine allergy, if you have had any reaction involving swelling, wheezing, or feeling faint, or if your allergies trigger asthma symptoms, because these situations may need testing, a specialist referral, and an emergency plan with adrenaline auto-injectors. New allergies appearing in adulthood are also worth assessing.
Some situations are emergencies and should not wait for an appointment. Call your local emergency number immediately if there is difficulty breathing, swelling of the lips, tongue, throat, or face, a widespread rash with faintness, persistent vomiting, or collapse, as these can be signs of anaphylaxis. Use an adrenaline auto-injector straight away if one is prescribed.