Which of the following are signs of dehydration in the skin?

Tightness, flakiness, and dullness are classic signs of dehydration in the skin. When skin is dehydrated, it lacks adequate moisture, leading to a tightening sensation as the skin becomes less supple. This can result in flakiness, where the outer layer of skin may peel or become rough. Additionally, dehydrated skin often appears dull due to the loss of radiance that occurs when the skin barrier is compromised and unable to reflect light effectively.

The other combinations of symptoms point toward different skin issues. A greasy texture and acne typically indicate excess oil production and potential blockages in the pores rather than dehydration. Redness and warmth may suggest inflammation or irritation, possibly related to various skin conditions or reactions rather than dehydration specifically. Extreme dryness and itchiness might suggest very dry skin or dermatitis but are not as directly associated with the subtle signs of dehydration as those listed in the correct answer.