Greasy hair suddenly!

[Lemmonie]

I am a nail tech but hoping you can help. I use the same shampoo, loreall professional silver and the conditioner. A week ago I noticed a greasy patch on the top of my head and assumed I hadn't washed it properly. Anyway I have taken care when washing (every day as I have done for years) to ensure I have washed it thoroughly and rinsed the hair clean of conditioner. But it's still very greasy in one patch.

Any idea why? And what shall I do?

Thanks