The symptoms of conjunctivitis will depend on the cause, but generally they include:

• eye redness: this happens as a result of the inflammation and widening of the tiny blood vessels in the conjunctiva (thin layer of cells that covers the front of the eyes)
• watering eyes: the conjunctiva contains thousands of cells that produce mucus and tiny glands that produce tears – inflammation causes the glands to become overactive, so that they water more than usual

Although only one eye tends to be affected at first, symptoms usually affect both eyes within a few hours.

Infective conjunctivitis

If you have infective conjunctivitis you may also have:

• a burning sensation in your eyes
• a feeling of grit in your eyes
• a sticky coating on the eyelashes – usually when you first wake in the morning
• an enlarged lymph node in front of the ear

Allergic conjunctivitis

You may also have itchy eyes if you have allergic conjunctivitis.  

The pattern of symptoms for allergic conjunctivitis depends on the substance you are allergic to.

Allergies to pollen (hay fever) occur during certain parts of the year. You can have an allergy to:

• tree pollen, released during spring
• grass pollen, released during the end of spring and beginning of summer
• weed pollen, released any time from early spring to late autumn

It is highly likely that the pollen will also cause other symptoms such as sneezing and a runny or blocked nose.

Allergies to dust mites or animal fur cause symptoms throughout the year. Both eyes are usually affected and you may find the symptoms worse in the morning.

Some people develop an allergy to eye drops. This is known as contact dermatoconjunctivitis and can also affect your eyelids, causing them to become dry and sore.

Some people are allergic to wearing contact lenses, which is known as giant papillary conjunctivitis. The symptoms progress much more slowly and you may also develop small spots on the inside of your upper eyelids. This type of conjunctivitis carries a high risk of complications so you need to get medical advice.

Read more information about allergies.

When to seek medical advice

Most cases of conjunctivitis are not a cause for concern but you should contact your GP if you think you have it – especially if you think the conjunctivitis is related to wearing contact lenses.

Your GP will be able to check whether there is a more serious underlying cause of your symptoms.

When to seek immediate medical advice

The following symptoms could be the sign of a more serious eye condition:

• pain in your eyes
• sensitivity to light (photophobia)
• disturbed vision
• intense redness in one or both of your eyes

If you experience any of these symptoms, contact your GP immediately. If this isn't possible, visit your nearest accident and emergency (A&E) department.

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.

Immune system

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

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.

Respiratory tract

The respiratory tract is a general term that is used to describe all the parts of the body that are involved in helping a person to breathe.