The aim of this clinical trial is to evaluate the effects of water-filtered Infrared-A radiation on patients suffering from hand osteoarthritis. The main questions it aims to answer are:

• Does water-filtered Infrared-A radiation reduce pain and improve the function of finger joints over time?
• Are patients satisfied with the treatment results when compared to those who were on a wait-list?

Inclusion Criteria:

• Diagnosis of finger polyarthritis (confirmed by a specialist, radiological findings available)
• Local pain for more than 50% of the day in the past 3 months.
• Subjective pain intensity of local pain in the last 24 hours on a VAS scale of 0 to 10 being >4.
• No planned local treatment in the next 6 months.
• No planned intra-articular injections within the next 6 months.
• The patient must be able to understand the study explanations and appropriately follow the instructions of the investigating physician.

Exclusion Criteria:

• Chronic inflammatory joint diseases.
• Poor general health.
• Febrile diseases.
• Fibromyalgia syndrome.
• Psychotic disorders.
• Severe comorbidities.
• Acute unclear skin diseases.
• Heat urticaria.
• Painful diseases/diagnoses of the shoulder and/or arm.
• Lymphatic vessel diseases (lymphedema, lymphangitis).
• Porphyria.
• Pain-associated diseases/diagnoses of the shoulder and/or arm.
• Intra-articular injections or arthroscopies within the last 3 months.
• Previous or planned surgical procedure on the affected joints in the last 8 weeks or in the upcoming 6 months.
• Intake or application of photosensitizing drugs or extracts (e.g., porphyrins, tetracyclines, sulfonamides, psoralenes, St. John's wort).
• Systemic medication with glucocorticoids or immunosuppressants.
• Pain medication with opioid analgesics.
• Known pregnancy.
• Concurrent participation in another clinical trial.