Why do acne scars randomly get red?

[Shizakhan]

The red is the inflammation that lingers after your acne has healed. This also depends on the colour of your skin. To reduce this, apply organic honey on the acne scars and drink a lot of water.

[Pinkwords]

I think need to put some oxy10 to kill the bacteria and dry it up.
Try to wash face in the morning and night - avoid fried food.

If it is very serious, would suggest you go for those clinic that provides acne cure. The one I went in Singapore is Radium Medical Aesthetics and their agnes acne elimination program is quite effective and good.