Third-stage syphilis is contagious. Clinically progressing to third-stage syphilis indicates a more serious condition, and indeed, third-stage syphilis is considered late-stage. Although it is less contagious compared to first and second-stage syphilis because the titer decreases as it progresses to this stage, it remains infectious. This means it is still possible to transmit to others. Therefore, patients with third-stage syphilis should receive timely treatment.