Cystic acne pop out on my head after i stop using Head and Shoulders shampoo

[Rotkiv]

I made a profile here just to ask if anyone has had a similar opinion. It has happened several times by now. After I stop using H&S shampoo (one type only) cystic acne appear on the scalp of my head. They are not painful but are rather big and full with gooy material. Then i start using it again and my scalp skin returns to normal. Does anyone know the ingredients they use in this shampoo and are there any side effects? This is very odd to me and i think it shouldn't be caused by a shampoo.
Thank you in advance