Vascular Issues: Poor blood flow to the penis can result from conditions like atherosclerosis, high blood pressure, or diabetes, leading to difficulty in achieving or maintaining an erection.

Neurological Disorders: Conditions affecting the nervous system, such as multiple sclerosis or Parkinson's disease, can interfere with the transmission of signals between the brain and the reproductive organs.

Hormonal Imbalance: An imbalance in hormones, especially testosterone, can impact erectile function. Conditions like hypogonadism (low testosterone) can contribute to ED.

Medications: Some medications, including certain antidepressants, antihypertensives, and antipsychotics, may have side effects that contribute to erectile dysfunction.

Psychological Factors: Stress, anxiety, depression, and other psychological issues can negatively affect sexual performance. Performance anxiety or relationship issues may also contribute to ED.

Smoking and Substance Abuse: Tobacco and recreational drug use can damage blood vessels and contribute to erectile dysfunction. Smoking, in particular, is a significant risk factor.

Lifestyle Factors: Sedentary lifestyle, obesity, and poor dietary habits can contribute to conditions like diabetes and cardiovascular disease, which are linked to erectile dysfunction.

Underlying Medical Conditions: Certain medical conditions, such as heart disease, kidney disease, and chronic obstructive pulmonary disease (COPD), can be associated with erectile dysfunction.

Penile Abnormalities: Structural abnormalities of the penis, such as Peyronie's disease, can affect blood flow and cause difficulties in achieving or maintaining an erection.

Age: While aging itself is not a direct cause, it often brings an increased risk of developing conditions (like diabetes or cardiovascular disease) that can contribute to erectile dysfunction.