How to get rid of hyperpigmentation from face and neck?

I am a 26 year male. I am from india. I was brown skinned when I was 21-22. But in recent time my face and neck has become darkest part of my body. body is still brownish but only face and neck is darkest. What can I do? I am using spf 30 but no improvement... I have also tried lemon juice on face but didn't work. Also can I use hydroquinone 4%? how to use it safely?

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