They occur when there's a not enough supply of oxygen to the cornea or the tissues covering the eyes. If they don't come with pain or impaired vision then they are not serious otherwise they might be an indication of a serious health issue!

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They can appear as a result of irritation, allergies, stress and so on and usually don't hurt.

Bloodshot eyes can appear at any time of the day though sometimes common in the morning but there are usually pointers or causes  (when they are not serious health issues).

They appear as a dense bloody area (due to the bleeding)caused when the small blood vessels on the eye surface become congested or enlarged, they look bad (almost alarming but they clear in a few days.

If you notice bloodshot eyes, the next time you wake up, it might be due to these five things:

1. Alcohol/Hangover

A good old hangover can be the simple reason behind a bloodshot eye if you wake up to one in the morning.

2. Make up products

Some makeup products have properties that irritate the eyes when applied (reason you should always look out for ingredients) and if this happens, the eyes can become bloodshot.

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3. Food

Some foods or a particular diet can cause the cornea irritated and consequently give a blood shot eye(s).

4. Reduce tear secretion

Tear constantly help keep the eye lubricated and clean but when a defect/reduction in tear secretion happens the eyes get dry and can get bloody around a certain area.

5. Sleep deprivation

Not getting enough sleep is usually a major cause of bloodshot eyes. When you don't get at least 5 hours of sleep, the eyes may become red as a result of less oxygen supplied to the cornea.