There are many scar treatments available on the market these days. With so many to compare though, it's difficult to know which is the most effective scar treatment for you and your scar. Ironically, many scar products also contain ingredients that cause allergic reactions like contact dermatitis.
The following scar treatments/ingredients can cause contact dermatitis:
Vitamin E (Tocopherol) - Topical vitamin E may be good for preventing sun-induced skin damage but it has NO effect on, and actually WORSENS the appearance of scars in up to 90% of adults. Up to 33% of users develop a contact dermatitis to vitamin E. American dermatologists and Canadian pediatricians recommend completely avoiding vitamin E scar products.
Hydroquinone - Hydroquinone can be very effective in helping to lighten dark scars. However, it is no longer sold in some countries because of its long-term use dangers. Though rare, hydroquinone can lead to a condition called ochronosis, even at its over-the-counter strength of 2%. Ochronosis is permanent hyper-pigmentation with sooty darkening of the skin. Ochronosis may also cause loss of skin elasticity and impaired wound healing. Other side effects of hydroquinone include contact dermatitis (rash, redness, itching and flaking) and nail discoloration. Some researchers have questioned whether hydroquinone and related compounds may even cause cancer. As a result of these fears, hydroquinone is only available by prescription in Europe and it is highly regulated in Asia. The skin-lightening effects of hydroquinone decrease with prolonged use and with sun exposure. Hydroquinone does not improve any other aspect of the scar other than the dark pigment.
Kojic Acid - like hydroquinone, kojic acid is effective in lightening dark scars, brown spots and even melasma. Unfotunately, some studies suggest that skin exposed to kojic acid on a regular basis becomes more sensitive. Skin sensitization can lead to allergic contact dermatitis. Like hydroquinone, koijic acid does not improve any other aspect of the scar other than the dark pigment.
The following scar treatments/ingredients are hypoallergenic:
Silicone Sheeting or Silicone Gel - Silicone will improve the appearance and texture of both an old and new problem scar. Silicone sheets are cumbersome and interfere with clothing and make-up. Silicone gel (Dimethicone) is as effective as silicone sheeting and is much easier to apply. Easy make-up and sun-block application is an added benefit of the gel. Dimethicone silicone gel has been certified as safe.
Vitamin C - One of the skin's main components is collagen. Scars heal through new collagen formation. Untreated skin produces unorganized, haphazard collagen. Vitamin C scars treatments help to improve and organize collagen formation. Improved collagen formation leads to faster and more cosmetic scar healing. Vitamin C also decreases inflammation and is used effectively to lighten dark scars. Vitamin C can cause stinging and even some mild flaking or redness until the skin "gets used to" the ascorbic acid (particularly with concentrations of 10-20%), but this is not an allergy.
Botanicals (Natural Plant Extracts) - Just because something is "natural" does not mean that it cannot cause an allergy. Having said that, many skin care products contain natural plant extracts as ingredients, mainly because of their anti-inflammatory effects. Safe examples of botanicals that improve scar appearance include:
Aloe Vera: - accelerates wound healing - decreases inflammation - stimulates new skin growth through amino acids - promotes healthy healing in the deepest skin layers
Linoleic Acid (Safflower Seed Oil) and Oleic Acid (Sunflower Seed Oil): - regenerate lipid biolayer crucial for skin moisture - improve wound healing - improve scar elasticity - control production of prostaglandins, one of the skin's main "building blocks." - prevent disturbance in prostaglandin production which causes poor healing - lighten dark pigment (hyper-pigmentation)
Licorice Extract: - strong anti-inflammatory - accelerates skin renewal - lightens dark scars and brown spots including melasma (especially when combined with a stable form of vitamin C) - anti-acne effects (both prevention and treatment)
In summary, safe scar therapy ingredients include vitamin C, dimethicone silicone and botanicals like aloe, licorice and some flower seed oils. All improve scar appearance, including dark scars, and have been shown to be safe for topical use. Compare frequently recommended scar treatments here.