Bleaching and dyeing hair are two different processes that alter the color of your hair but involve distinct mechanisms and purposes:

Hair Bleaching:

• Purpose: Bleaching removes the existing color (melanin) from your hair, usually to make it lighter or to prepare it for coloring with a lighter shade than your natural hair color. It oxidizes the hair's pigment using a combination of hydrogen peroxide and an alkaline agent, effectively lifting the color.
• Process: Bleaching breaks down the melanin particles within the hair shaft, turning them into colorless substances that wash out, resulting in lighter hair. Depending on the initial hair color and the strength of the bleach, it may take multiple applications to achieve a significant lightening effect.
• Effects: Bleaching can lead to dryness, brittleness, and potential structural damage to the hair because it disrupts the hair cuticle and strips away natural oils. It can also reveal underlying warm tones (yellow, orange) before reaching a pale blonde stage.

Hair Dyeing:

• Purpose: Dyeing involves depositing color onto the hair to change or enhance its hue, whether darkening, lightening, or adding tonal variations. It can be used to cover gray hairs, add highlights, or achieve a completely new color.
• Process: Hair dyes contain pigments that attach themselves to the hair strands, replacing or enhancing the existing color. There are permanent, semi-permanent, and demi-permanent dyes, each with varying degrees of longevity and intensity.
• Types: Direct dyes (semi-permanent) coat the hair without penetrating deeply, while oxidative dyes (permanent and demi-permanent) require a developer (hydrogen peroxide) to activate the color molecules that then penetrate and bond with the hair structure.
• Effects: Dyeing can also impact the health of your hair, particularly with frequent use or strong chemicals, but it doesn't generally cause as much damage as bleaching unless it involves lifting the hair color significantly.

In summary, bleaching lightens hair by removing its natural pigments, while dyeing changes hair color by adding new pigments. Sometimes, bleaching is a preliminary step before dyeing if one wishes to go several shades lighter than their current hair color.