Which of the following is most important to check before a chemical hair service?

Before performing a chemical hair service, the most crucial aspect to check is the client's allergy history. This is essential because chemical hair services often involve the use of strong agents, such as dyes, relaxers, or perm solutions, that can provoke allergic reactions in some individuals. Understanding a client's allergy history helps in identifying any potential risks and ensures their safety during the treatment.

A thorough assessment of allergy history allows professionals to avoid using specific products that could cause adverse reactions, which can range from mild irritation to serious health concerns. Additionally, it fosters trust and good communication between the client and the cosmetologist, which is vital for a successful service.

While evaluating a client's hair type, scalp condition, and hair color preference is also important, these factors primarily influence the application technique and desired outcome but do not directly address the immediate health risks associated with allergies. Therefore, the emphasis on allergy history plays a pivotal role in safeguarding the client's well-being during chemical hair treatments.