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The lymph nodes could have swollen up due to allergic reaction to the bleach and dye. This is usually due to PPD OR ParaPhenyleneDiamine. Take any OTC antiallergic such as Benadryl. Wash hair and scalp thoroughly with a mild shampoo and 2% hydrogen peroxide solution. Compress the hair and scalp with potassium permanganate in a 1:5000 dilution, to completely oxidize the PPD. A wet dressing of olive oil and lime may be used. Corticosteroid cream can also be applied. Also consult your doctor immediately regarding this. Take care!
You could be allergic to the hair dye that was used. I would keep an eye on it, and if it gets worse go see a dr.