4. Allergies
Allergies are one of the most common causes of bloodshot eyes, and if you’re allergic to anything around you, you’ll usually manifest with other symptoms that are common of allergy cases; these symptoms can include itching and reddening of the skin, and it’s not always restricted to the site where the allergic component touched the skin in the case of a contact allergy.
Allergies can happen because of many different things, including allergies to pollen (which sees hay fever happen as the wind picks up, or one is exposed to any type of pollen from flowers, fruit or plants through other ways), or it can happen because of something you touched (like poison ivy) or something you ate (like shellfish or nuts).
Remember that you can be exposed to especially food allergies just through mild content, even when the physical meal or snack only contains a trace of the allergen.