What Are the Thermal Damage to Skin Signs/ Symptoms?

Your question about thermal damage does not explain why you are asking the question.  Is this just academic interest or are you concerned about something after laser treatment?

Some heating of the dermis (such as bulk heating) can be beneficial as it can stimulate production of cytokines, and/or heat shock proteins which can lead to production of new collagen in your skin

However over heating can produce a thermal injury which is undesirable as it can lead to healing problems.

lasers, radiofrequency devices, plasma sources and ultrasound energy delivers heat into the dermis while often bypassing injury to the epidermis.  Some wavelengths of lasers are better suited to be used for this purpose, as they are not absorbed preferentially by the epidermis thereby minimizing hyper and hypopigmentation risks, burns, etc.  The heat that is generated in the dermis stimulates new collagen production and can help the body get rid of sundamaged dermal collagen that exists currently and may be a contributing factor to wrinkles. In addition there is improvement of the damaged elastic fibers.  The energy is calibrated in joules/cm2, or fluence.  The thermal relaxation time was a concept pioneered by Dr. Rox Anderson and involves the timing of the microsecond laser pulse to be less than the time needed to heat up an epidermal cell.  In this way, energy can affect the target without damaging the good cells.  Stacked pulses can be done safely some not all lasers.  As an example, the 595 nm. pulsed dye laser, the V-beam laser, is used for treatment of facial blood vessels, rosacea, port wine stains (congenital red birthmarks) and triple stacking can be done on some stubborn vessels if the correct parameters of that laser are chosen but there could be a risk of a blister and skin changes if not careful. The V-beam laser uses a cold spray on the skin before the laser strikes, during and after, to minimize the burning and stinging and protect the epidermis from pigment change.

The fluence is in joules / cm 2. It is the amount of enery per area you are delivering. If you want to attack a sun spot you want the energy to heat the spot but not the surrounding area. The thermal relaxation time is important as well. Thethermal relaxation time (tr) of a heated region of tissue is the time required for the peak temperature rise (
Tpeak) in a heated region of tissue to decrease to 37% of the total rise. You won't need to know this as a patient though. Skins of damage include persistent redness after Intense pulse light, skin breakdown, blister formation, and increased pain during the treatment.