Dry Eye Syndrome: This is a common condition, especially in young adults, and can be caused by prolonged screen time, dry environments, or makeup use. It presents with irritation, redness, and sometimes a gritty sensation without necessarily affecting vision.

Allergic Conjunctivitis: Given the age and presentation, allergic reactions to pollen, dust, or other environmental allergens are common and can cause eye irritation, redness, and itching.
Blepharitis: Inflammation of the eyelids can cause irritation, redness, and sometimes a burning sensation. It's often associated with poor eyelid hygiene or conditions like rosacea.
Conjunctivitis (Viral or Bacterial): Although the question specifies no trauma, viral or bacterial conjunctivitis (pink eye) can occur without a clear source of infection and presents with redness, discharge, and irritation.

Acute Angle-Closure Glaucoma: Although less common and typically presents with severe vision changes and pain, it's crucial to rule out due to its potential for permanent vision loss if not promptly treated.
Uveitis: Inflammation of the uvea can present with eye pain, redness, and light sensitivity. It has various causes, including autoimmune diseases, and requires prompt treatment to prevent complications.
Corneal Ulcer: An infection of the cornea that can result from contact lens use or other minor trauma not recalled by the patient. It presents with pain, redness, and decreased vision.

Sjögren's Syndrome: An autoimmune disorder that can cause dry eyes among other symptoms. It's less common but should be considered in patients with persistent dry eye symptoms without another clear cause.
Thygeson's Superficial Punctate Keratitis: A condition characterized by recurrent episodes of superficial punctate keratitis, often associated with viral infections or autoimmune conditions.
Erythema Multiforme: A skin condition that can also affect the eyes, presenting with target lesions and sometimes eye irritation. It's often triggered by infections or medications.