Jessica Alba is defending the quality of her Honest Company's sunscreen, following a public flogging from disgruntled customers who complained of suffering burns after applying the lotion.

Photos of sunburned heads, backs and chests posted on Twitter have gone viral in the last few days.

An investigation into consumer complaints by NBC 5 Chicago found that while most sunscreens contain about 18 to 25 per cent of zinc oxide, The Honest Company reformulated their sunscreens, decreasing levels to 9.3 per cent.

"Protecting our loved ones and yours is the reason we founded The Honest Company," Alba and co-founder Christopher Gavigan said in a statement on their blog. "As parents, it pains us to hear that anyone has had a negative experience with our Sunscreen."

And in a statement to People magazine, the company stood by the product, saying that the number of complaints received about the sunscreen constitute a fraction of units sold.

“Our sunscreen lotion was tested, by an independent third-party, against the protocols prescribed by the U.S. Food & Drug Administration's (FDA) monograph for over-the-counter sunscreen products. The results showed that our product is effective and safe for use...," the company said.