You might refer to it as "sleep" or "eye gunk" - but whatever you call it, most of us wake up with a bit of crust in the corners of our eyes. It's such a routine part of our morning that we barely think of it.

However, eye health experts caution that it may not always be as harmless as it appears. While often benign, the colour, texture, and quantity of this morning build-up can sometimes provide hints about your health, reports Plymouth Live.

Neil Laird, Specialist Optometrist from Pure Optical, explains what your morning eye discharge is really indicating, and when it could be a signal to take action. "Eye discharge is a normal part of the body's cleaning process," he said. "It's your eyes' way of flushing out debris, oils, and dead cells while you sleep, but if it suddenly changes in appearance or comes with other symptoms, it could be a sign that something more serious is going on."

Below we give a rundown of the different kinds of sleep in your eyes - and which ones should worry us the most.

This type of discharge is a natural blend of oils, mucus, and skin cells that your eyes produce overnight to help clear out debris. The colour may vary slightly depending on factors such as eye dryness, allergies, or the use of oil-based skincare before bed.

However, if you notice that the amount suddenly increases or it appears alongside pain, swelling, or changes in your vision, it's best to get it checked by an optometrist.

A hefty amount of white discharge, coupled with redness or swelling, could be a sign of viral conjunctivitis or, in some instances, ocular herpes. Viral conjunctivitis often resolves itself, though soothing eye drops may be needed to ease discomfort.

Ocular herpes, however, needs immediate treatment to prevent potential long-term damage to the cornea.

While makeup residue can occasionally result in green or grey discharge, the presence of itchiness, redness, and blurred vision alongside this colour sleep usually indicates a bacterial infection or bacterial conjunctivitis (also known as 'pink eye'), which will require a course of antibiotics to clear up.

Yellow discharge can also indicate an infection, but it could suggest other conditions such as a stye, which is a painful red lump on the lash line that sometimes oozes thick yellow fluid. Another possibility is a blocked tear duct, which causes swelling in the inner corner of the eye along with discharge.

In more severe cases, dacryocystitis, an infection of the tear duct due to a build-up of stagnant fluid, can produce watery mucus with small yellow lumps from the inner corner of the eye.

The glands in the eye are delicate and can easily become clogged by the wrong products, such as certain creams or makeup, so it's vital you clean your eyes thoroughly after wearing makeup and use only eye-safe products that are not too heavy or oily.

A red or pink discharge from the eyes can often be a sign of minor irritation, possibly due to dryness or slight internal bleeding. While this might not be a cause for concern in some instances, regular occurrences could suggest damage to the eye surface or surrounding tissues, warranting an immediate trip to the optician.

It's crucial not to dismiss sudden changes in morning discharge, particularly if it's heavy, discoloured, or accompanied by swelling, pain, or blurred vision. "Your eyes are a fantastic early warning system for your overall health," Mr Laird points out.

"By paying attention to subtle changes, you can catch infections or eye conditions early before they become more serious."

To maintain optimal eye health and prevent issues, Mr Laird has offered some tips:

"Eye health often gets overlooked until something goes wrong," he warned. "But small changes can be your body's way of raising a red flag. The earlier you act, the easier it is to protect your vision and prevent lasting damage."

What 'sleep' in your eyes in the morning actually means - and when to worry - The Mirror