* Change in Formulation: The manufacturer might have changed the ingredients in the hair dye since you last used it. Even a small change can trigger an allergic reaction.
* Increased Sensitivity: You might have developed a sensitivity or allergy over time. Repeated exposure to allergens can sometimes lead to your immune system reacting differently.
* New Allergens: You could have developed a new allergy to an ingredient commonly found in hair dye, such as paraphenylenediamine (PPD), which is a common culprit.
* Compromised Skin Barrier: If your scalp is irritated, damaged, or has open cuts, it can make you more susceptible to allergic reactions.
* Build-up: Residue of products containing hair dye may have built up over time.
* Expired Product: The dye may have expired, leading to changes in its chemical composition.