Raynaud's phenomenon (or syndrome) manifests in two primary forms:

1. Primary Raynaud's Phenomenon: This is the most common form, often referred to as 'idiopathic' because it typically has no identifiable underlying cause. It frequently affects women under 30 years of age and generally presents as a mild condition that patients can manage without significant medical intervention.

2. Secondary Raynaud's Phenomenon: This form is generally more complex and severe than Primary Raynaud's. It is typically associated with underlying medical conditions, most commonly autoimmune disorders such as rheumatoid arthritis, scleroderma, and systemic lupus erythematosus (SLE or lupus).