Newly Updated --Understanding MCS is an accessible introduction to Multiple Chemical Sensitivity, Environmental Illness, and mast cell related disorders that is aligned with the DSM-5. Written primarily for therapists--social workers, mental health counselors, expressive/creative arts therapists, psychologists--it is intended to inform all clinicians and healthcare professionals on how to recognize environmental illnesses and the signs and symptoms with which clients may present. Understanding MCS offers DSM-5 assessments and coding for these hard to recognize and often difficult to manage chronic diseases as well as providing client-focused supports, guidelines for reasonable accommodations, insights regarding treatment planning, and practical suggestions for ways to adapt counseling practices in order to best serve individuals living with these chronic illnesses.