Hello and welcome to HCM,
A photo of the rash or bruise will be more informative.
There are various causes of rash and a bruise on upper thigh.
Bruise is caused by bleeding in the
soft tissue.
Rash can be due to infection most commonly viral infection.
Is there any history of trauma to the upper thigh?
Is there history of fever?
A history of trauma favors a bruise.
Bruise caused by trauma takes couple of days to disappear.
Trauma can lead to swelling which may be painful for few days.
This type of swelling is called hematoma.
Infections causing rash are commonly viral and they are associated with fever.
Spontaneously occurring rashes occur due to disorders of clotting factors.
Thus, I suggest you get some investigations -
platelet count,
bleeding time, clotting time,
prothrombin time and activated
partial thromboplastin time.
If case there is some abnormality of clotting pathway, these investigations will be deranged.
Thanks and take care
Dr Shailja Puri