Identifying the causes of a red eye remains a significant clinical challenge, as it is crucial not to overlook an ophthalmological emergency. The causes are varied, ranging from benign conditions to serious diseases that may threaten vision. Based on current evidence, this article aims to provide primary care physicians with clear and relevant clinical guidelines to help them identify situations requiring urgent ophthalmological care. Taking a focused medical history, identifying red flags and performing a standardized clinical examination are essential. The article also offers tailored treatment strategies for each common cause of a red eye. Rapid referral to an ophthalmologist is essential in cases of uncertainty or severity.