The photo shows a red, tender spot on the inner lower eyelid. It may be an internal stye (hordeolum), which is an inflamed or infected eyelid oil gland that can form a painful spot on the inside of the lid. But a photo cannot rule out other eye-surface problems.

Because the eye itself is quite red and there is pain, arrange an urgent examination today or within 24 hours with an eye doctor/optometrist or clinician, especially for a 16-year-old.

Until seen:

Get same-day emergency care if there is blurred/decreased vision, light sensitivity, severe or worsening pain, fever, swelling spreading around the eye, trouble moving the eye, significant discharge/pus, injury/foreign body, or headache with nausea. These symptoms need assessment because painful red eyes can sometimes be more serious than a stye. The NHS stye guidance recommends urgent review if it is very painful, swollen, affects vision, produces pus, or infection appears to spread. The NHS eye-pain advice also flags severe pain, a very red eye, light sensitivity, or vision changes as urgent.

An internal hordeolum can present as a tender, red, sometimes pus-containing spot on the inner eyelid, whereas a chalazion is more often a firmer, less painful blocked gland. Pfenninger and Fowler's Procedures for Primary Care, p. 2701.