Epididymitis: This condition, often caused by bacterial infection, can present with scrotal pain even in the absence of significant swelling or erythema, especially in its early stages. The pain can be severe and is usually localized to the epididymis.

Orchitis: Inflammation of one or both testicles, usually caused by viral or bacterial infections. It can cause scrotal pain without significant swelling or erythema, especially if the inflammation is mild.
Spermatocele or Epididymal Cyst: These are benign cysts that can cause intermittent or chronic scrotal pain due to their size or position, without necessarily causing swelling or erythema.
Varicocele: An enlargement of the veins within the scrotum, similar to varicose veins. It can cause a dull, aching pain, especially later in the day, without significant swelling or erythema.

Testicular Torsion: Although it typically presents with acute onset of severe pain, swelling, and erythema, in some cases, especially early on, these signs might be minimal or absent. It's a surgical emergency, making it crucial not to miss.
Appendix Testis Torsion (Hydatid of Morgagni): Similar to testicular torsion, this condition involves the twisting of a small appendage attached to the testis. It can present with sudden onset of pain but might not always have significant swelling or erythema.

Henoch-Schönlein Purpura (HSP): A form of vasculitis that can affect various parts of the body, including the scrotum, causing pain. It's more common in children but can occur in adults. The scrotal involvement might not always be accompanied by the typical purpura seen in other parts of the body.
Scrotal Neuroma: A rare benign tumor of the nerve tissue within the scrotum, which can cause chronic pain without significant swelling or erythema.
Referred Pain: Pain referred from other areas, such as the lower back or abdomen, due to nerve pathways. Conditions like a herniated disk or abdominal pathology can cause scrotal pain without local signs of inflammation.