Conjunctivitis, allergic

Conjunctivitis is inflammation (swelling) of the conjunctiva. The conjunctiva is the transparent membrane (thin layer of cells) that covers the white part of the eyeball and the inner surfaces of the eyelids.

There are three different types of conjunctivitis, each with a different cause. The three types are:

• irritant conjunctivitis
• infective conjunctivitis
• allergic conjunctivitis

Irritant conjunctivitis

Irritant conjunctivitis occurs when an irritant, such as chlorine (a chemical that is often used to purify water) or an eyelash, gets into the eyes and makes them sore. Rubbing the eyes can make the condition worse. The conjunctivitis should settle once the irritant is removed. If the eyes are very red and painful, medical attention should be sought immediately.

Infective conjunctivitis

Infective conjunctivitis is caused by a virus, bacteria or a sexually transmitted infection (STI), such as chlamydia or gonorrhoea. The most common symptoms include reddening and watering of the eyes, and a sticky coating on the eyelashes. See Infective conjunctivitis for more information.

Allergic conjunctivitis

Allergic conjunctivitis occurs when the eyes come into contact with an allergen. An allergen is a substance, such as pollen or animal fur, that makes the immune system (the body’s defence system) react abnormally. This causes irritation and inflammation, known as an allergic reaction. Allergic conjunctivitis causes itchy, swollen eyes.

There are four main types of allergic conjunctivitis:

• seasonal allergic conjunctivitis
• perennial allergic conjunctivitis
• contact dermatoconjunctivitis
• giant papillary conjunctivitis

These are caused by different allergens and may have slightly different symptoms. For more information, see Symptoms of allergic conjunctivitis.

How common is allergic conjunctivitis?

Allergic conjunctivitis is responsible for 15% of all eye-related problems that are recorded in GP surgeries. There are four to five cases of allergic conjunctivitis for every 1,000 people every year in the UK.

Half of all cases of allergic conjunctivitis are seasonal allergic conjunctivitis, which is commonly caused by grass pollen.

If seasonal or perennial allergic conjunctivitis also includes other symptoms, such as sneezing and an itchy nose, this could be hay fever, which affects around 20% of people in the UK. See Hay fever for more information.

Giant papillary conjunctivitis is experienced by 1-5% of people using soft contact lenses and 1% of people using hard contact lenses.

Outlook

Seasonal and perennial allergic conjunctivitis can interfere with day-to-day life because they are usually triggered by common allergens, such as pollen. However, they can usually be managed effectively with medication, such as antihistamines.

Contact dermatoconjunctivitis and giant papillary conjunctivitis are usually caused by eye drops or contact lenses. Once the cause is identified and avoided, the symptoms usually clear up. However, it may be necessary to see an ophthalmologist (a medical doctor who specialises in eye conditions), who can provide advice about any further treatments that are needed.

Glossary

Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Allergy
Allergy is the term used to describe an adverse (bad) reaction that the body has to a particular substance.

Allergen
An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.

Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some are good for you.

Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.