These signs may reveal an underlying disease requiring medical diagnosis.

How to prevent spontaneous bruising?
Promote a diet rich in vitamins C and K to strengthen your blood vessels.
Drink enough water to maintain good skin elasticity.
Avoid self-medication, especially with blood-switching medicines.
Protect your skin, especially if it is thin and sensitive, by wearing appropriate clothing.
Conclusion

Blues that appear for no reason can be benign, but they can also reveal an imbalance or a health problem.

Listen to your body: if it sends you unusual signals, do not ignore them.

Simply paying attention to your diet and lifestyle may often be enough to limit these inconveniences.
And if the doubt persists, medical advice will help you to see more clearly.