I've had hair straightening or rebonding treatment thrice now. What to do?

I didn't go for hair spas and this has damaged my hair. They're brittle and damaged right now. People are suggesting me to go for keratin or cystein but I'm very worried due to high levels of formaldehyde chemicals present in the products. Already my poor hair have underwent so much chemical treatment and I get them colored from a L'oreal hair dye frequently too. What should I do now? Let them be and apply natural masks and practise home remedies or go for keratin etc?

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