Secondary Syphilis: This condition is known for causing painless, erythematous macules or papules on the palms and soles, among other symptoms. The patient's age and lack of medical history make this a plausible diagnosis, especially if the patient has been sexually active.

Palmar Psoriasis: Although psoriasis can be painful, some cases may present with minimal discomfort. The erythematous macules on the palms could be indicative of palmar psoriasis, especially if the patient has a family history or other signs of psoriasis.
Pityriasis Rosea: While less common on the palms, pityriasis rosea can cause erythematous macules and is often seen in young adults. The lack of pain and the specific location might make this less likely, but it remains a consideration.
Contact Dermatitis: Allergic or irritant contact dermatitis could cause erythematous macules on the palms, especially if the patient has recently been exposed to new substances or has a job that involves handling potential irritants.

Syphilis (repeated for emphasis): Given the potential for serious complications if left untreated, syphilis must be ruled out, even if other diagnoses seem more likely.
Lyme Disease: Although less common, Lyme disease can cause erythema migrans, which might be mistaken for erythematous macules. The patient's history of tick exposure or outdoor activities would increase the likelihood of this diagnosis.
Viral Exanthem: Certain viral infections can cause widespread rashes, including on the palms. While these are often accompanied by other symptoms, it's crucial to consider viral etiologies, especially if the patient has been in contact with someone who has a similar illness.

Keratoderma Blennorrhagicum: Associated with reactive arthritis, this condition causes vesiculopustular eruptions on the palms and soles, which could initially be mistaken for erythematous macules.
Palmoplantar Erythrodysesthesia: A rare condition often associated with chemotherapy, characterized by redness, swelling, and sometimes peeling of the skin on the palms and soles. Given the patient's age and lack of medical history, this would be an unlikely diagnosis without additional context.
Graft-Versus-Host Disease (GVHD): In patients who have undergone bone marrow or stem cell transplants, GVHD can cause skin manifestations, including erythematous macules on the palms. This diagnosis would be extremely rare in a 23-year-old without a history of such procedures.