Hair is Thin After Highlighting

I am a 47 year old woman who had slight graying hair. My hairdresser talked me into highlighting my hair. She used a volume 20 bleach and a toner. 24 hours later I had itching, burning and swelling and saw my allergist. He put me on prednisone for a week and cortisone lotions. A month later my hair feels like cotton as the strands of hair are thinner, breaking off at the crown and generally coming out at the root after washing/combing.

What if anything can I now do? Obviously, I will never again use chemicals on my hair.

You have likely had a chemical Alopecia (hair loss) with a skin reaction. I know exactly what you are going through (having had a spiral perm in the eighties with the same thing happen) and although it is likely all your hair will grow back just as it was, it will take time, especially if you wear your hair long. Avoiding harsh shampoos and conditioning your hair regularly may help the hair that is there, but little will help it grow faster which is what really needs to happen. Concealing options like hats, scarves, and Toppik are all options as well. If this condition persists past 6 months, I would recommend a follow-up visit to your doctor to determine if anything else is going on.